BIND 9 configuration is broadly similar
to BIND 8; however, there are a few new
areas
of configuration, such as views. BIND
8 configuration files should work with few alterations in BIND
9, although more complex configurations should be reviewed to check
if they can be more efficiently implemented using the new features
found in BIND 9.

BIND 4 configuration files can be
converted to the new format
using the shell script
contrib/named-bootconf/named-bootconf.sh.

Configuration File Elements

Following is a list of elements used throughout the BIND configuration
file documentation:

A named list of one or more ip_addr
with optional key_id and/or
ip_port.
A masters_list may include other
masters_lists.

domain_name

A quoted string which will be used as
a DNS name, for example "my.test.domain".

namelist

A list of one or more domain_name
elements.

dotted_decimal

One to four integers valued 0 through
255 separated by dots (`.'), such as 123,
45.67 or 89.123.45.67.

ip4_addr

An IPv4 address with exactly four elements
in dotted_decimal notation.

ip6_addr

An IPv6 address, such as 2001:db8::1234.
IPv6 scoped addresses that have ambiguity on their
scope zones must be disambiguated by an appropriate
zone ID with the percent character (`%') as
delimiter. It is strongly recommended to use
string zone names rather than numeric identifiers,
in order to be robust against system configuration
changes. However, since there is no standard
mapping for such names and identifier values,
currently only interface names as link identifiers
are supported, assuming one-to-one mapping between
interfaces and links. For example, a link-local
address fe80::1 on the link
attached to the interface ne0
can be specified as fe80::1%ne0.
Note that on most systems link-local addresses
always have the ambiguity, and need to be
disambiguated.

ip_addr

An ip4_addr or ip6_addr.

ip_port

An IP port number.
The number is limited to 0
through 65535, with values
below 1024 typically restricted to use by processes running
as root.
In some cases, an asterisk (`*') character can be used as a
placeholder to
select a random high-numbered port.

ip_prefix

An IP network specified as an ip_addr,
followed by a slash (`/') and then the number of bits in the
netmask.
Trailing zeros in a ip_addr
may omitted.
For example, 127/8 is the
network 127.0.0.0 with
netmask 255.0.0.0 and 1.2.3.0/28 is
network 1.2.3.0 with netmask 255.255.255.240.

When specifying a prefix involving a IPv6 scoped address
the scope may be omitted. In that case the prefix will
match packets from any scope.

key_id

A domain_name representing
the name of a shared key, to be used for transaction
security.

key_list

A list of one or more
key_ids,
separated by semicolons and ending with a semicolon.

number

A non-negative 32-bit integer
(i.e., a number between 0 and 4294967295, inclusive).
Its acceptable value might further
be limited by the context in which it is used.

path_name

A quoted string which will be used as
a pathname, such as zones/master/my.test.domain.

port_list

A list of an ip_port or a port
range.
A port range is specified in the form of
range followed by
two ip_ports,
port_low and
port_high, which represents
port numbers from port_low through
port_high, inclusive.
port_low must not be larger than
port_high.
For example,
range 1024 65535 represents
ports from 1024 through 65535.
In either case an asterisk (`*') character is not
allowed as a valid ip_port.

size_spec

A 64-bit unsigned integer, or the keywords
unlimited or
default.

Integers may take values
0 <= value <= 18446744073709551615, though
certain parameters
(such as max-journal-size) may
use a more limited range within these extremes.
In most cases, setting a value to 0 does not
literally mean zero; it means "undefined" or
"as big as possible", depending on the context.
See the explanations of particular parameters
that use size_spec
for details on how they interpret its use.

Numeric values can optionally be followed by a
scaling factor:
K or k
for kilobytes,
M or m
for megabytes, and
G or g
for gigabytes, which scale by 1024, 1024*1024, and
1024*1024*1024 respectively.

unlimited generally means
"as big as possible", though in certain contexts,
(including max-cache-size), it may
mean the largest possible 32-bit unsigned integer
(0xffffffff); this distinction can be important when
dealing with larger quantities.
unlimited is usually the best way
to safely set a very large number.

default
uses the limit that was in force when the server was started.

yes_or_no

Either yes or no.
The words true and false are
also accepted, as are the numbers 1
and 0.

dialup_option

One of yes,
no, notify,
notify-passive, refresh or
passive.
When used in a zone, notify-passive,
refresh, and passive
are restricted to slave and stub zones.

Address Match Lists

Syntax

Definition and Usage

Address match lists are primarily used to determine access
control for various server operations. They are also used in
the listen-on and sortlist
statements. The elements which constitute an address match
list can be any of the following:

an IP address (IPv4 or IPv6)

an IP prefix (in `/' notation)

a key ID, as defined by the key
statement

the name of an address match list defined with
the acl statement

a nested address match list enclosed in braces

Elements can be negated with a leading exclamation mark (`!'),
and the match list names "any", "none", "localhost", and
"localnets" are predefined. More information on those names
can be found in the description of the acl statement.

The addition of the key clause made the name of this syntactic
element something of a misnomer, since security keys can be used
to validate access without regard to a host or network address.
Nonetheless, the term "address match list" is still used
throughout the documentation.

When a given IP address or prefix is compared to an address
match list, the comparison takes place in approximately O(1)
time. However, key comparisons require that the list of keys
be traversed until a matching key is found, and therefore may
be somewhat slower.

The interpretation of a match depends on whether the list is being
used for access control, defining listen-on ports, or in a
sortlist, and whether the element was negated.

When used as an access control list, a non-negated match
allows access and a negated match denies access. If
there is no match, access is denied. The clauses
allow-notify,
allow-recursion,
allow-recursion-on,
allow-query,
allow-query-on,
allow-query-cache,
allow-query-cache-on,
allow-transfer,
allow-update,
allow-update-forwarding, and
blackhole all use address match
lists. Similarly, the listen-on option will cause the
server to refuse queries on any of the machine's
addresses which do not match the list.

Order of insertion is significant. If more than one element
in an ACL is found to match a given IP address or prefix,
preference will be given to the one that came
first in the ACL definition.
Because of this first-match behavior, an element that
defines a subset of another element in the list should
come before the broader element, regardless of whether
either is negated. For example, in
1.2.3/24; ! 1.2.3.13;
the 1.2.3.13 element is completely useless because the
algorithm will match any lookup for 1.2.3.13 to the 1.2.3/24
element. Using ! 1.2.3.13; 1.2.3/24 fixes
that problem by having 1.2.3.13 blocked by the negation, but
all other 1.2.3.* hosts fall through.

Comment Syntax

The BIND 9 comment syntax allows for
comments to appear
anywhere that whitespace may appear in a BIND configuration
file. To appeal to programmers of all kinds, they can be written
in the C, C++, or shell/perl style.

Syntax

/* This is a BIND comment as in C */

// This is a BIND comment as in C++

# This is a BIND comment as in common UNIX shells
# and perl

Definition and Usage

Comments may appear anywhere that whitespace may appear in
a BIND configuration file.

C-style comments start with the two characters /* (slash,
star) and end with */ (star, slash). Because they are completely
delimited with these characters, they can be used to comment only
a portion of a line or to span multiple lines.

C-style comments cannot be nested. For example, the following
is not valid because the entire comment ends with the first */:

/* This is the start of a comment.
This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */
This is no longer in any comment. */

C++-style comments start with the two characters // (slash,
slash) and continue to the end of the physical line. They cannot
be continued across multiple physical lines; to have one logical
comment span multiple lines, each line must use the // pair.
For example:

// This is the start of a comment. The next line
// is a new comment, even though it is logically
// part of the previous comment.

Shell-style (or perl-style, if you prefer) comments start
with the character # (number sign)
and continue to the end of the
physical line, as in C++ comments.
For example:

# This is the start of a comment. The next line
# is a new comment, even though it is logically
# part of the previous comment.

Warning

You cannot use the semicolon (`;') character
to start a comment such as you would in a zone file. The
semicolon indicates the end of a configuration
statement.

Configuration File Grammar

A BIND 9 configuration consists of
statements and comments.
Statements end with a semicolon. Statements and comments are the
only elements that can appear without enclosing braces. Many
statements contain a block of sub-statements, which are also
terminated with a semicolon.

The following statements are supported:

acl

defines a named IP address
matching list, for access control and other uses.

controls

declares control channels to be used
by the rndc utility.

include

includes a file.

key

specifies key information for use in
authentication and authorization using TSIG.

logging

specifies what the server logs, and where
the log messages are sent.

lwres

configures named to
also act as a light-weight resolver daemon (lwresd).

masters

defines a named masters list for
inclusion in stub and slave zone masters clauses.

lists DNSSEC keys to be kept up to date
using RFC 5011 trust anchor maintenance.

view

defines a view.

zone

defines a zone.

The logging and
options statements may only occur once
per
configuration.

acl Statement Grammar

acl acl-name {
address_match_list
};

acl Statement Definition and
Usage

The acl statement assigns a symbolic
name to an address match list. It gets its name from a primary
use of address match lists: Access Control Lists (ACLs).

Note that an address match list's name must be defined
with acl before it can be used
elsewhere; no forward references are allowed.

The following ACLs are built-in:

any

Matches all hosts.

none

Matches no hosts.

localhost

Matches the IPv4 and IPv6 addresses of all network
interfaces on the system. When addresses are
added or removed, the localhost
ACL element is updated to reflect the changes.

localnets

Matches any host on an IPv4 or IPv6 network
for which the system has an interface.
When addresses are added or removed,
the localnets
ACL element is updated to reflect the changes.
Some systems do not provide a way to determine the prefix
lengths of
local IPv6 addresses.
In such a case, localnets
only matches the local
IPv6 addresses, just like localhost.

controls Statement Definition and
Usage

The controls statement declares control
channels to be used by system administrators to control the
operation of the name server. These control channels are
used by the rndc utility to send
commands to and retrieve non-DNS results from a name server.

An inet control channel is a TCP socket
listening at the specified ip_port on the
specified ip_addr, which can be an IPv4 or IPv6
address. An ip_addr of * (asterisk) is
interpreted as the IPv4 wildcard address; connections will be
accepted on any of the system's IPv4 addresses.
To listen on the IPv6 wildcard address,
use an ip_addr of ::.
If you will only use rndc on the local host,
using the loopback address (127.0.0.1
or ::1) is recommended for maximum security.

If no port is specified, port 953 is used. The asterisk
"*" cannot be used for ip_port.

The ability to issue commands over the control channel is
restricted by the allow and
keys clauses.
Connections to the control channel are permitted based on the
address_match_list. This is for simple
IP address based filtering only; any key_id
elements of the address_match_list
are ignored.

A unix control channel is a UNIX domain
socket listening at the specified path in the file system.
Access to the socket is specified by the perm,
owner and group clauses.
Note on some platforms (SunOS and Solaris) the permissions
(perm) are applied to the parent directory
as the permissions on the socket itself are ignored.

If no controls statement is present,
named will set up a default
control channel listening on the loopback address 127.0.0.1
and its IPv6 counterpart ::1.
In this case, and also when the controls statement
is present but does not have a keys clause,
named will attempt to load the command channel key
from the file rndc.key in
/etc (or whatever sysconfdir
was specified as when BIND was built).
To create a rndc.key file, run
rndc-confgen -a.

The rndc.key feature was created to
ease the transition of systems from BIND 8,
which did not have digital signatures on its command channel
messages and thus did not have a keys clause.
It makes it possible to use an existing BIND 8
configuration file in BIND 9 unchanged,
and still have rndc work the same way
ndc worked in BIND 8, simply by executing the
command rndc-confgen -a after BIND 9 is
installed.

Since the rndc.key feature
is only intended to allow the backward-compatible usage of
BIND 8 configuration files, this
feature does not
have a high degree of configurability. You cannot easily change
the key name or the size of the secret, so you should make a
rndc.conf with your own key if you
wish to change
those things. The rndc.key file
also has its
permissions set such that only the owner of the file (the user that
named is running as) can access it.
If you
desire greater flexibility in allowing other users to access
rndc commands, then you need to create
a
rndc.conf file and make it group
readable by a group
that contains the users who should have access.

To disable the command channel, use an empty
controls statement:
controls { };.

include Statement Grammar

includefilename;

include Statement Definition and
Usage

The include statement inserts the
specified file at the point where the include
statement is encountered. The include
statement facilitates the administration of configuration
files
by permitting the reading or writing of some things but not
others. For example, the statement could include private keys
that are readable only by the name server.

key Statement Grammar

keykey_id {
algorithm string;
secret string;
};

key Statement Definition and Usage

The key statement can occur at the
top level
of the configuration file or inside a view
statement. Keys defined in top-level key
statements can be used in all views. Keys intended for use in
a controls statement
(see the section called “controls Statement Definition and
Usage”)
must be defined at the top level.

The key_id, also known as the
key name, is a domain name uniquely identifying the key. It can
be used in a server
statement to cause requests sent to that
server to be signed with this key, or in address match lists to
verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.

The algorithm_id is a string
that specifies a security/authentication algorithm. Named
supports hmac-md5,
hmac-sha1, hmac-sha224,
hmac-sha256, hmac-sha384
and hmac-sha512 TSIG authentication.
Truncated hashes are supported by appending the minimum
number of required bits preceded by a dash, e.g.
hmac-sha1-80. The
secret_string is the secret
to be used by the algorithm, and is treated as a base-64
encoded string.

logging Statement Definition and
Usage

The logging statement configures a
wide
variety of logging options for the name server. Its channel phrase
associates output methods, format options and severity levels with
a name that can then be used with the category phrase
to select how various classes of messages are logged.

Only one logging statement is used to
define
as many channels and categories as are wanted. If there is no logging statement,
the logging configuration will be:

In BIND 9, the logging configuration
is only established when
the entire configuration file has been parsed. In BIND 8, it was
established as soon as the logging
statement
was parsed. When the server is starting up, all logging messages
regarding syntax errors in the configuration file go to the default
channels, or to standard error if the "-g" option
was specified.

The channel Phrase

All log output goes to one or more channels;
you can make as many of them as you want.

Every channel definition must include a destination clause that
says whether messages selected for the channel go to a file, to a
particular syslog facility, to the standard error stream, or are
discarded. It can optionally also limit the message severity level
that will be accepted by the channel (the default is
info), and whether to include a
named-generated time stamp, the
category name
and/or severity level (the default is not to include any).

The null destination clause
causes all messages sent to the channel to be discarded;
in that case, other options for the channel are meaningless.

The file destination clause directs
the channel
to a disk file. It can include limitations
both on how large the file is allowed to become, and how many
versions
of the file will be saved each time the file is opened.

If you use the versions log file
option, then
named will retain that many backup
versions of the file by
renaming them when opening. For example, if you choose to keep
three old versions
of the file lamers.log, then just
before it is opened
lamers.log.1 is renamed to
lamers.log.2, lamers.log.0 is renamed
to lamers.log.1, and lamers.log is
renamed to lamers.log.0.
You can say versions unlimited to
not limit
the number of versions.
If a size option is associated with
the log file,
then renaming is only done when the file being opened exceeds the
indicated size. No backup versions are kept by default; any
existing
log file is simply appended.

The size option for files is used
to limit log
growth. If the file ever exceeds the size, then named will
stop writing to the file unless it has a versions option
associated with it. If backup versions are kept, the files are
rolled as
described above and a new one begun. If there is no
versions option, no more data will
be written to the log
until some out-of-band mechanism removes or truncates the log to
less than the
maximum size. The default behavior is not to limit the size of
the
file.

The syslog destination clause
directs the
channel to the system log. Its argument is a
syslog facility as described in the syslog man
page. Known facilities are kern, user,
mail, daemon, auth,
syslog, lpr, news,
uucp, cron, authpriv,
ftp, local0, local1,
local2, local3, local4,
local5, local6 and
local7, however not all facilities
are supported on
all operating systems.
How syslog will handle messages
sent to
this facility is described in the syslog.conf man
page. If you have a system which uses a very old version of syslog that
only uses two arguments to the openlog() function,
then this clause is silently ignored.

On Windows machines syslog messages are directed to the EventViewer.

The severity clause works like syslog's
"priorities", except that they can also be used if you are writing
straight to a file rather than using syslog.
Messages which are not at least of the severity level given will
not be selected for the channel; messages of higher severity
levels
will be accepted.

If you are using syslog, then the syslog.conf priorities
will also determine what eventually passes through. For example,
defining a channel facility and severity as daemon and debug but
only logging daemon.warning via syslog.conf will
cause messages of severity info and
notice to
be dropped. If the situation were reversed, with named writing
messages of only warning or higher,
then syslogd would
print all messages it received from the channel.

The stderr destination clause
directs the
channel to the server's standard error stream. This is intended
for
use when the server is running as a foreground process, for
example
when debugging a configuration.

The server can supply extensive debugging information when
it is in debugging mode. If the server's global debug level is
greater
than zero, then debugging mode will be active. The global debug
level is set either by starting the named server
with the -d flag followed by a positive integer,
or by running rndc trace.
The global debug level
can be set to zero, and debugging mode turned off, by running rndc
notrace. All debugging messages in the server have a debug
level, and higher debug levels give more detailed output. Channels
that specify a specific debug severity, for example:

channel specific_debug_level {
file "foo";
severity debug 3;
};

will get debugging output of level 3 or less any time the
server is in debugging mode, regardless of the global debugging
level. Channels with dynamic
severity use the
server's global debug level to determine what messages to print.

If print-time has been turned on,
then
the date and time will be logged. print-time may
be specified for a syslog channel,
but is usually
pointless since syslog also logs
the date and
time. If print-category is
requested, then the
category of the message will be logged as well. Finally, if print-severity is
on, then the severity level of the message will be logged. The print- options may
be used in any combination, and will always be printed in the
following
order: time, category, severity. Here is an example where all
three print- options
are on:

The default_debug channel has the
special
property that it only produces output when the server's debug
level is
nonzero. It normally writes to a file called named.run
in the server's working directory.

For security reasons, when the "-u"
command line option is used, the named.run file
is created only after named has
changed to the
new UID, and any debug output generated while named is
starting up and still running as root is discarded. If you need
to capture this output, you must run the server with the "-g"
option and redirect standard error to a file.

Once a channel is defined, it cannot be redefined. Thus you
cannot alter the built-in channels directly, but you can modify
the default logging by pointing categories at channels you have
defined.

The category Phrase

There are many categories, so you can send the logs you want
to see wherever you want, without seeing logs you don't want. If
you don't specify a list of channels for a category, then log
messages
in that category will be sent to the default category
instead. If you don't specify a default category, the following
"default default" is used:

category default { default_syslog; default_debug; };

As an example, let's say you want to log security events to
a file, but you also want keep the default logging behavior. You'd
specify the following:

Following are the available categories and brief descriptions
of the types of log information they contain. More
categories may be added in future BIND releases.

default

The default category defines the logging
options for those categories where no specific
configuration has been
defined.

general

The catch-all. Many things still aren't
classified into categories, and they all end up here.

database

Messages relating to the databases used
internally by the name server to store zone and cache
data.

security

Approval and denial of requests.

config

Configuration file parsing and processing.

resolver

DNS resolution, such as the recursive
lookups performed on behalf of clients by a caching name
server.

xfer-in

Zone transfers the server is receiving.

xfer-out

Zone transfers the server is sending.

notify

The NOTIFY protocol.

client

Processing of client requests.

unmatched

Messages that named was unable to determine the
class of or for which there was no matching view.
A one line summary is also logged to the client category.
This category is best sent to a file or stderr, by
default it is sent to
the null channel.

network

Network operations.

update

Dynamic updates.

update-security

Approval and denial of update requests.

queries

Specify where queries should be logged to.

At startup, specifying the category queries will also
enable query logging unless querylog option has been
specified.

The query log entry reports the client's IP
address and port number, and the query name,
class and type. Next it reports whether the
Recursion Desired flag was set (+ if set, -
if not set), if the query was signed (S),
EDNS was in use (E), if TCP was used (T), if
DO (DNSSEC Ok) was set (D), or if CD (Checking
Disabled) was set (C). After this the
destination address the query was sent to is
reported.

client 127.0.0.1#62536: query: www.example.com IN AAAA +SE

client ::1#62537: query: www.example.net IN AAAA -SE

query-errors

Information about queries that resulted in some
failure.

dispatch

Dispatching of incoming packets to the
server modules where they are to be processed.

dnssec

DNSSEC and TSIG protocol processing.

lame-servers

Lame servers. These are misconfigurations
in remote servers, discovered by BIND 9 when trying to
query those servers during resolution.

delegation-only

Delegation only. Logs queries that have been
forced to NXDOMAIN as the result of a
delegation-only zone or a
delegation-only in a
forward, hint or stub zone declaration.

edns-disabled

Log queries that have been forced to use plain
DNS due to timeouts. This is often due to
the remote servers not being RFC 1034 compliant
(not always returning FORMERR or similar to
EDNS queries and other extensions to the DNS
when they are not understood). In other words, this is
targeted at servers that fail to respond to
DNS queries that they don't understand.

Note: the log message can also be due to
packet loss. Before reporting servers for
non-RFC 1034 compliance they should be re-tested
to determine the nature of the non-compliance.
This testing should prevent or reduce the
number of false-positive reports.

Note: eventually named will have to stop
treating such timeouts as due to RFC 1034 non
compliance and start treating it as plain
packet loss. Falsely classifying packet
loss as due to RFC 1034 non compliance impacts
on DNSSEC validation which requires EDNS for
the DNSSEC records to be returned.

The query-errors Category

The query-errors category is
specifically intended for debugging purposes: To identify
why and how specific queries result in responses which
indicate an error.
Messages of this category are therefore only logged
with debug levels.

At the debug levels of 1 or higher, each response with the
rcode of SERVFAIL is logged as follows:

This means an error resulting in SERVFAIL was
detected at line 3880 of source file
query.c.
Log messages of this level will particularly
help identify the cause of SERVFAIL for an
authoritative server.

At the debug levels of 2 or higher, detailed context
information of recursive resolutions that resulted in
SERVFAIL is logged.
The log message will look like as follows:

The first part before the colon shows that a recursive
resolution for AAAA records of www.example.com completed
in 30.000183 seconds and the final result that led to the
SERVFAIL was determined at line 2970 of source file
resolver.c.

The following part shows the detected final result and the
latest result of DNSSEC validation.
The latter is always success when no validation attempt
is made.
In this example, this query resulted in SERVFAIL probably
because all name servers are down or unreachable, leading
to a timeout in 30 seconds.
DNSSEC validation was probably not attempted.

The last part enclosed in square brackets shows statistics
information collected for this particular resolution
attempt.
The domain field shows the deepest zone
that the resolver reached;
it is the zone where the error was finally detected.
The meaning of the other fields is summarized in the
following table.

referral

The number of referrals the resolver received
throughout the resolution process.
In the above example this is 2, which are most
likely com and example.com.

restart

The number of cycles that the resolver tried
remote servers at the domain
zone.
In each cycle the resolver sends one query
(possibly resending it, depending on the response)
to each known name server of
the domain zone.

qrysent

The number of queries the resolver sent at the
domain zone.

timeout

The number of timeouts since the resolver
received the last response.

lame

The number of lame servers the resolver detected
at the domain zone.
A server is detected to be lame either by an
invalid response or as a result of lookup in
BIND9's address database (ADB), where lame
servers are cached.

neterr

The number of erroneous results that the
resolver encountered in sending queries
at the domain zone.
One common case is the remote server is
unreachable and the resolver receives an ICMP
unreachable error message.

badresp

The number of unexpected responses (other than
lame) to queries sent by the
resolver at the domain zone.

adberr

Failures in finding remote server addresses
of the domain zone in the ADB.
One common case of this is that the remote
server's name does not have any address records.

findfail

Failures of resolving remote server addresses.
This is a total number of failures throughout
the resolution process.

valfail

Failures of DNSSEC validation.
Validation failures are counted throughout
the resolution process (not limited to
the domain zone), but should
only happen in domain.

At the debug levels of 3 or higher, the same messages
as those at the debug 1 level are logged for other errors
than SERVFAIL.
Note that negative responses such as NXDOMAIN are not
regarded as errors here.

At the debug levels of 4 or higher, the same messages
as those at the debug 2 level are logged for other errors
than SERVFAIL.
Unlike the above case of level 3, messages are logged for
negative responses.
This is because any unexpected results can be difficult to
debug in the recursion case.

lwres Statement Definition and Usage

The lwres statement configures the
name
server to also act as a lightweight resolver server. (See
the section called “Running a Resolver Daemon”.) There may be multiple
lwres statements configuring
lightweight resolver servers with different properties.

The listen-on statement specifies a
list of
IPv4 addresses (and ports) that this instance of a lightweight
resolver daemon
should accept requests on. If no port is specified, port 921 is
used.
If this statement is omitted, requests will be accepted on
127.0.0.1,
port 921.

The view statement binds this
instance of a
lightweight resolver daemon to a view in the DNS namespace, so that
the
response will be constructed in the same manner as a normal DNS
query
matching this view. If this statement is omitted, the default view
is
used, and if there is no default view, an error is triggered.

The search statement is equivalent to
the
search statement in
/etc/resolv.conf. It provides a
list of domains
which are appended to relative names in queries.

The ndots statement is equivalent to
the
ndots statement in
/etc/resolv.conf. It indicates the
minimum
number of dots in a relative domain name that should result in an
exact match lookup before search path elements are appended.

options Statement Definition and
Usage

The options statement sets up global
options
to be used by BIND. This statement
may appear only
once in a configuration file. If there is no options
statement, an options block with each option set to its default will
be used.

attach-cache

Allows multiple views to share a single cache
database.
Each view has its own cache database by default, but
if multiple views have the same operational policy
for name resolution and caching, those views can
share a single cache to save memory and possibly
improve resolution efficiency by using this option.

The attach-cache option
may also be specified in view
statements, in which case it overrides the
global attach-cache option.

The cache_name specifies
the cache to be shared.
When the named server configures
views which are supposed to share a cache, it
creates a cache with the specified name for the
first view of these sharing views.
The rest of the views will simply refer to the
already created cache.

One common configuration to share a cache would be to
allow all views to share a single cache.
This can be done by specifying
the attach-cache as a global
option with an arbitrary name.

Another possible operation is to allow a subset of
all views to share a cache while the others to
retain their own caches.
For example, if there are three views A, B, and C,
and only A and B should share a cache, specify the
attach-cache option as a view A (or
B)'s option, referring to the other view name:

Views that share a cache must have the same policy
on configurable parameters that may affect caching.
The current implementation requires the following
configurable options be consistent among these
views:
check-names,
cleaning-interval,
dnssec-accept-expired,
dnssec-validation,
max-cache-ttl,
max-ncache-ttl,
max-cache-size, and
zero-no-soa-ttl.

Note that there may be other parameters that may
cause confusion if they are inconsistent for
different views that share a single cache.
For example, if these views define different sets of
forwarders that can return different answers for the
same question, sharing the answer does not make
sense or could even be harmful.
It is administrator's responsibility to ensure
configuration differences in different views do
not cause disruption with a shared cache.

directory

The working directory of the server.
Any non-absolute pathnames in the configuration file will be
taken
as relative to this directory. The default location for most
server
output files (e.g. named.run)
is this directory.
If a directory is not specified, the working directory
defaults to `.', the directory from
which the server
was started. The directory specified should be an absolute
path.

key-directory

When performing dynamic update of secure zones, the
directory where the public and private DNSSEC key files
should be found, if different than the current working
directory. (Note that this option has no effect on the
paths for files containing non-DNSSEC keys such as
bind.keys,
rndc.key or
session.key.)

managed-keys-directory

Specifies the directory in which to store the files that
track managed DNSSEC keys. By default, this is the working
directory.

If named is not configured to use views,
then managed keys for the server will be tracked in a single
file called managed-keys.bind.
Otherwise, managed keys will be tracked in separate files,
one file per view; each file name will be the SHA256 hash
of the view name, followed by the extension
.mkeys.

named-xfer

This option is obsolete. It
was used in BIND 8 to specify
the pathname to the named-xfer
program. In BIND 9, no separate
named-xfer program is needed;
its functionality is built into the name server.

tkey-gssapi-keytab

The KRB5 keytab file to use for GSS-TSIG updates. If
this option is set and tkey-gssapi-credential is not
set, then updates will be allowed with any key
matching a principal in the specified keytab.

tkey-gssapi-credential

The security credential with which the server should
authenticate keys requested by the GSS-TSIG protocol.
Currently only Kerberos 5 authentication is available
and the credential is a Kerberos principal which the
server can acquire through the default system key
file, normally /etc/krb5.keytab.
The location keytab file can be overridden using the
tkey-gssapi-keytab option. Normally this principal is
of the form "DNS/server.domain".
To use GSS-TSIG, tkey-domain must
also be set if a specific keytab is not set with
tkey-gssapi-keytab.

tkey-domain

The domain appended to the names of all shared keys
generated with TKEY. When a
client requests a TKEY exchange,
it may or may not specify the desired name for the
key. If present, the name of the shared key will
be client specified part +
tkey-domain. Otherwise, the
name of the shared key will be random hex
digits + tkey-domain.
In most cases, the domainname
should be the server's domain name, or an otherwise
non-existent subdomain like
"_tkey.domainname". If you are
using GSS-TSIG, this variable must be defined, unless
you specify a specific keytab using tkey-gssapi-keytab.

tkey-dhkey

The Diffie-Hellman key used by the server
to generate shared keys with clients using the Diffie-Hellman
mode
of TKEY. The server must be
able to load the
public and private keys from files in the working directory.
In
most cases, the keyname should be the server's host name.

cache-file

This is for testing only. Do not use.

dump-file

The pathname of the file the server dumps
the database to when instructed to do so with
rndc dumpdb.
If not specified, the default is named_dump.db.

memstatistics-file

The pathname of the file the server writes memory
usage statistics to on exit. If not specified,
the default is named.memstats.

pid-file

The pathname of the file the server writes its process ID
in. If not specified, the default is
/var/run/named/named.pid.
The PID file is used by programs that want to send signals to
the running
name server. Specifying pid-file none disables the
use of a PID file — no file will be written and any
existing one will be removed. Note that none
is a keyword, not a filename, and therefore is not enclosed
in
double quotes.

recursing-file

The pathname of the file the server dumps
the queries that are currently recursing when instructed
to do so with rndc recursing.
If not specified, the default is named.recursing.

statistics-file

The pathname of the file the server appends statistics
to when instructed to do so using rndc stats.
If not specified, the default is named.stats in the
server's current directory. The format of the file is
described
in the section called “The Statistics File”.

bindkeys-file

The pathname of a file to override the built-in trusted
keys provided by named.
See the discussion of dnssec-lookaside
and dnssec-validation for details.
If not specified, the default is
/etc/bind.keys.

secroots-file

The pathname of the file the server dumps
security roots to when instructed to do so with
rndc secroots.
If not specified, the default is
named.secroots.

session-keyfile

The pathname of the file into which to write a TSIG
session key generated by named for use by
nsupdate -l. If not specified, the
default is /var/run/named/session.key.
(See the section called “Dynamic Update Policies”, and in
particular the discussion of the
update-policy statement's
local option for more
information about this feature.)

session-keyname

The key name to use for the TSIG session key.
If not specified, the default is "local-ddns".

session-keyalg

The algorithm to use for the TSIG session key.
Valid values are hmac-sha1, hmac-sha224, hmac-sha256,
hmac-sha384, hmac-sha512 and hmac-md5. If not
specified, the default is hmac-sha256.

port

The UDP/TCP port number the server uses for
receiving and sending DNS protocol traffic.
The default is 53. This option is mainly intended for server
testing;
a server using a port other than 53 will not be able to
communicate with
the global DNS.

random-device

The source of entropy to be used by the server. Entropy is
primarily needed
for DNSSEC operations, such as TKEY transactions and dynamic
update of signed
zones. This options specifies the device (or file) from which
to read
entropy. If this is a file, operations requiring entropy will
fail when the
file has been exhausted. If not specified, the default value
is
/dev/random
(or equivalent) when present, and none otherwise. The
random-device option takes
effect during
the initial configuration load at server startup time and
is ignored on subsequent reloads.

preferred-glue

If specified, the listed type (A or AAAA) will be emitted
before other glue
in the additional section of a query response.
The default is not to prefer any type (NONE).

root-delegation-only

Turn on enforcement of delegation-only in TLDs
(top level domains) and root zones with an optional
exclude list.

DS queries are expected to be made to and be answered by
delegation only zones. Such queries and responses are
treated as an exception to delegation-only processing
and are not converted to NXDOMAIN responses provided
a CNAME is not discovered at the query name.

If a delegation only zone server also serves a child
zone it is not always possible to determine whether
an answer comes from the delegation only zone or the
child zone. SOA NS and DNSKEY records are apex
only records and a matching response that contains
these records or DS is treated as coming from a
child zone. RRSIG records are also examined to see
if they are signed by a child zone or not. The
authority section is also examined to see if there
is evidence that the answer is from the child zone.
Answers that are determined to be from a child zone
are not converted to NXDOMAIN responses. Despite
all these checks there is still a possibility of
false negatives when a child zone is being served.

Similarly false positives can arise from empty nodes
(no records at the name) in the delegation only zone
when the query type is not ANY.

Note some TLDs are not delegation only (e.g. "DE", "LV",
"US" and "MUSEUM"). This list is not exhaustive.

Disable the specified DNSSEC algorithms at and below the
specified name.
Multiple disable-algorithms
statements are allowed.
Only the most specific will be applied.

dnssec-lookaside

When set, dnssec-lookaside provides the
validator with an alternate method to validate DNSKEY
records at the top of a zone. When a DNSKEY is at or
below a domain specified by the deepest
dnssec-lookaside, and the normal DNSSEC
validation has left the key untrusted, the trust-anchor
will be appended to the key name and a DLV record will be
looked up to see if it can validate the key. If the DLV
record validates a DNSKEY (similarly to the way a DS
record does) the DNSKEY RRset is deemed to be trusted.

If dnssec-lookaside is set to
auto, then built-in default
values for the DLV domain and trust anchor will be
used, along with a built-in key for validation.

If dnssec-lookaside is set to
no, then dnssec-lookaside
is not used.

The default DLV key is stored in the file
bind.keys;
named will load that key at
startup if dnssec-lookaside is set to
auto. A copy of the file is
installed along with BIND 9, and is
current as of the release date. If the DLV key expires, a
new copy of bind.keys can be downloaded
from https://www.isc.org/solutions/dlv/.

(To prevent problems if bind.keys is
not found, the current key is also compiled in to
named. Relying on this is not
recommended, however, as it requires named
to be recompiled with a new key when the DLV key expires.)

NOTE: named only loads certain specific
keys from bind.keys: those for the
DLV zone and for the DNS root zone. The file cannot be
used to store keys for other zones.

dnssec-must-be-secure

Specify hierarchies which must be or may not be secure
(signed and validated). If yes,
then named will only accept answers if
they are secure. If no, then normal
DNSSEC validation applies allowing for insecure answers to
be accepted. The specified domain must be under a
trusted-keys or
managed-keys statement, or
dnssec-lookaside must be active.

dns64

This directive instructs named to
return mapped IPv4 addresses to AAAA queries when
there are no AAAA records. It is intended to be
used in conjunction with a NAT64. Each
dns64 defines one DNS64 prefix.
Multiple DNS64 prefixes can be defined.

Additionally a reverse IP6.ARPA zone will be created for
the prefix to provide a mapping from the IP6.ARPA names
to the corresponding IN-ADDR.ARPA names using synthesized
CNAMEs. dns64-server and
dns64-contact can be used to specify
the name of the server and contact for the zones. These
are settable at the view / options level. These are
not settable on a per-prefix basis.

Each dns64 supports an optional
clients ACL that determines which
clients are affected by this directive. If not defined,
it defaults to any;.

Each dns64 supports an optional
mapped ACL that selects which
IPv4 addresses are to be mapped in the corresponding
A RRset. If not defined it defaults to
any;.

Normally, DNS64 won't apply to a domain name that
owns one or more AAAA records; these records will
simply be returned. The optional
exclude ACL allows specification
of a list of IPv6 addresses that will be ignored
if they appear in a domain name's AAAA records, and
DNS64 will be applied to any A records the domain
name owns. If not defined, exclude
defaults to none.

A optional suffix can also
be defined to set the bits trailing the mapped
IPv4 address bits. By default these bits are
set to ::. The bits
matching the prefix and mapped IPv4 address
must be zero.

If recursive-only is set to
yes the DNS64 synthesis will
only happen for recursive queries. The default
is no.

If break-dnssec is set to
yes the DNS64 synthesis will
happen even if the result, if validated, would
cause a DNSSEC validation failure. If this option
is set to no (the default), the DO
is set on the incoming query, and there are RRSIGs on
the applicable records, then synthesis will not happen.

Boolean Options

allow-new-zones

If yes, then zones can be
added at runtime via rndc addzone
or deleted via rndc delzone.
The default is no.

auth-nxdomain

If yes, then the AA bit
is always set on NXDOMAIN responses, even if the server is
not actually
authoritative. The default is no;
this is
a change from BIND 8. If you
are using very old DNS software, you
may need to set it to yes.

deallocate-on-exit

This option was used in BIND
8 to enable checking
for memory leaks on exit. BIND 9 ignores the option and always performs
the checks.

memstatistics

Write memory statistics to the file specified by
memstatistics-file at exit.
The default is no unless
'-m record' is specified on the command line in
which case it is yes.

dialup

If yes, then the
server treats all zones as if they are doing zone transfers
across
a dial-on-demand dialup link, which can be brought up by
traffic
originating from this server. This has different effects
according
to zone type and concentrates the zone maintenance so that
it all
happens in a short interval, once every heartbeat-interval and
hopefully during the one call. It also suppresses some of
the normal
zone maintenance traffic. The default is no.

The dialup option
may also be specified in the view and
zone statements,
in which case it overrides the global dialup
option.

If the zone is a master zone, then the server will send out a
NOTIFY
request to all the slaves (default). This should trigger the
zone serial
number check in the slave (providing it supports NOTIFY)
allowing the slave
to verify the zone while the connection is active.
The set of servers to which NOTIFY is sent can be controlled
by
notify and also-notify.

If the
zone is a slave or stub zone, then the server will suppress
the regular
"zone up to date" (refresh) queries and only perform them
when the
heartbeat-interval expires in
addition to sending
NOTIFY requests.

Finer control can be achieved by using
notify which only sends NOTIFY
messages,
notify-passive which sends NOTIFY
messages and
suppresses the normal refresh queries, refresh
which suppresses normal refresh processing and sends refresh
queries
when the heartbeat-interval
expires, and
passive which just disables normal
refresh
processing.

This option is obsolete.
In BIND 8, fetch-glue yes
caused the server to attempt to fetch glue resource records
it
didn't have when constructing the additional
data section of a response. This is now considered a bad
idea
and BIND 9 never does it.

flush-zones-on-shutdown

When the nameserver exits due receiving SIGTERM,
flush or do not flush any pending zone writes. The default
is
flush-zones-on-shutdownno.

has-old-clients

This option was incorrectly implemented
in BIND 8, and is ignored by BIND 9.
To achieve the intended effect
of
has-old-clientsyes, specify
the two separate options auth-nxdomainyes
and rfc2308-type1no instead.

host-statistics

In BIND 8, this enables keeping of
statistics for every host that the name server interacts
with.
Not implemented in BIND 9.

maintain-ixfr-base

This option is obsolete.
It was used in BIND 8 to
determine whether a transaction log was
kept for Incremental Zone Transfer. BIND 9 maintains a transaction
log whenever possible. If you need to disable outgoing
incremental zone
transfers, use provide-ixfrno.

minimal-responses

If yes, then when generating
responses the server will only add records to the authority
and additional data sections when they are required (e.g.
delegations, negative responses). This may improve the
performance of the server.
The default is no.

multiple-cnames

This option was used in BIND 8 to allow
a domain name to have multiple CNAME records in violation of
the DNS standards. BIND 9.2 onwards
always strictly enforces the CNAME rules both in master
files and dynamic updates.

notify

If yes (the default),
DNS NOTIFY messages are sent when a zone the server is
authoritative for
changes, see the section called “Notify”. The messages are
sent to the
servers listed in the zone's NS records (except the master
server identified
in the SOA MNAME field), and to any servers listed in the
also-notify option.

If master-only, notifies are only
sent
for master zones.
If explicit, notifies are sent only
to
servers explicitly listed using also-notify.
If no, no notifies are sent.

The notify option may also be
specified in the zone
statement,
in which case it overrides the options notify statement.
It would only be necessary to turn off this option if it
caused slaves
to crash.

notify-to-soa

If yes do not check the nameservers
in the NS RRset against the SOA MNAME. Normally a NOTIFY
message is not sent to the SOA MNAME (SOA ORIGIN) as it is
supposed to contain the name of the ultimate master.
Sometimes, however, a slave is listed as the SOA MNAME in
hidden master configurations and in that case you would
want the ultimate master to still send NOTIFY messages to
all the nameservers listed in the NS RRset.

recursion

If yes, and a
DNS query requests recursion, then the server will attempt
to do
all the work required to answer the query. If recursion is
off
and the server does not already know the answer, it will
return a
referral response. The default is
yes.
Note that setting recursion no does not prevent
clients from getting data from the server's cache; it only
prevents new data from being cached as an effect of client
queries.
Caching may still occur as an effect the server's internal
operation, such as NOTIFY address lookups.
See also fetch-glue above.

request-nsid

If yes, then an empty EDNS(0)
NSID (Name Server Identifier) option is sent with all
queries to authoritative name servers during iterative
resolution. If the authoritative server returns an NSID
option in its response, then its contents are logged in
the resolver category at level
info.
The default is no.

rfc2308-type1

Setting this to yes will
cause the server to send NS records along with the SOA
record for negative
answers. The default is no.

Note

Not yet implemented in BIND
9.

use-id-pool

This option is obsolete.
BIND 9 always allocates query
IDs from a pool.

zone-statistics

If yes, the server will collect
statistical data on all zones (unless specifically turned
off
on a per-zone basis by specifying zone-statistics no
in the zone statement).
The default is no.
These statistics may be accessed
using rndc stats, which will
dump them to the file listed
in the statistics-file. See
also the section called “The Statistics File”.

This option was used in BIND
8 to make
the server treat carriage return ("\r") characters the same way
as a space or tab character,
to facilitate loading of zone files on a UNIX system that
were generated
on an NT or DOS machine. In BIND 9, both UNIX "\n"
and NT/DOS "\r\n" newlines
are always accepted,
and the option is ignored.

additional-from-auth, additional-from-cache

These options control the behavior of an authoritative
server when
answering queries which have additional data, or when
following CNAME
and DNAME chains.

When both of these options are set to yes
(the default) and a
query is being answered from authoritative data (a zone
configured into the server), the additional data section of
the
reply will be filled in using data from other authoritative
zones
and from the cache. In some situations this is undesirable,
such
as when there is concern over the correctness of the cache,
or
in servers where slave zones may be added and modified by
untrusted third parties. Also, avoiding
the search for this additional data will speed up server
operations
at the possible expense of additional queries to resolve
what would
otherwise be provided in the additional section.

For example, if a query asks for an MX record for host foo.example.com,
and the record found is "MX 10 mail.example.net", normally the address
records (A and AAAA) for mail.example.net will be provided as well,
if known, even though they are not in the example.com zone.
Setting these options to no
disables this behavior and makes
the server only search for additional data in the zone it
answers from.

These options are intended for use in authoritative-only
servers, or in authoritative-only views. Attempts to set
them to no without also
specifying
recursion no will cause the
server to
ignore the options and log a warning message.

Specifying additional-from-cache no actually
disables the use of the cache not only for additional data
lookups
but also when looking up the answer. This is usually the
desired
behavior in an authoritative-only server where the
correctness of
the cached data is an issue.

When a name server is non-recursively queried for a name
that is not
below the apex of any served zone, it normally answers with
an
"upwards referral" to the root servers or the servers of
some other
known parent of the query name. Since the data in an
upwards referral
comes from the cache, the server will not be able to provide
upwards
referrals when additional-from-cache no
has been specified. Instead, it will respond to such
queries
with REFUSED. This should not cause any problems since
upwards referrals are not required for the resolution
process.

match-mapped-addresses

If yes, then an
IPv4-mapped IPv6 address will match any address match
list entries that match the corresponding IPv4 address.

This option was introduced to work around a kernel quirk
in some operating systems that causes IPv4 TCP
connections, such as zone transfers, to be accepted on an
IPv6 socket using mapped addresses. This caused address
match lists designed for IPv4 to fail to match. However,
named now solves this problem
internally. The use of this option is discouraged.

filter-aaaa-on-v4

This option is only available when
BIND 9 is compiled with the
--enable-filter-aaaa option on the
"configure" command line. It is intended to help the
transition from IPv4 to IPv6 by not giving IPv6 addresses
to DNS clients unless they have connections to the IPv6
Internet. This is not recommended unless absolutely
necessary. The default is no.
The filter-aaaa-on-v4 option
may also be specified in view statements
to override the global filter-aaaa-on-v4
option.

If yes,
the DNS client is at an IPv4 address, in filter-aaaa,
and if the response does not include DNSSEC signatures,
then all AAAA records are deleted from the response.
This filtering applies to all responses and not only
authoritative responses.

If break-dnssec,
then AAAA records are deleted even when dnssec is enabled.
As suggested by the name, this makes the response not verify,
because the DNSSEC protocol is designed detect deletions.

This mechanism can erroneously cause other servers to
not give AAAA records to their clients.
A recursing server with both IPv6 and IPv4 network connections
that queries an authoritative server using this mechanism
via IPv4 will be denied AAAA records even if its client is
using IPv6.

This mechanism is applied to authoritative as well as
non-authoritative records.
A client using IPv4 that is not allowed recursion can
erroneously be given AAAA records because the server is not
allowed to check for A records.

Some AAAA records are given to IPv4 clients in glue records.
IPv4 clients that are servers can then erroneously
answer requests for AAAA records received via IPv4.

ixfr-from-differences

When yes and the server loads a new version of a master
zone from its zone file or receives a new version of a slave
file by a non-incremental zone transfer, it will compare
the new version to the previous one and calculate a set
of differences. The differences are then logged in the
zone's journal file such that the changes can be transmitted
to downstream slaves as an incremental zone transfer.

By allowing incremental zone transfers to be used for
non-dynamic zones, this option saves bandwidth at the
expense of increased CPU and memory consumption at the
master.
In particular, if the new version of a zone is completely
different from the previous one, the set of differences
will be of a size comparable to the combined size of the
old and new zone version, and the server will need to
temporarily allocate memory to hold this complete
difference set.

ixfr-from-differences
also accepts master and
slave at the view and options
levels which causes
ixfr-from-differences to be enabled for
all master or
slave zones respectively.
It is off by default.

multi-master

This should be set when you have multiple masters for a zone
and the
addresses refer to different machines. If yes, named will
not log
when the serial number on the master is less than what named
currently
has. The default is no.

dnssec-enable

Enable DNSSEC support in named. Unless set to yes,
named behaves as if it does not support DNSSEC.
The default is yes.

dnssec-validation

Enable DNSSEC validation in named.
Note dnssec-enable also needs to be
set to yes to be effective.
If set to no, DNSSEC validation
is disabled. If set to auto,
DNSSEC validation is enabled, and a default
trust-anchor for the DNS root zone is used. If set to
yes, DNSSEC validation is enabled,
but a trust anchor must be manually configured using
a trusted-keys or
managed-keys statement. The default
is yes.

dnssec-accept-expired

Accept expired signatures when verifying DNSSEC signatures.
The default is no.
Setting this option to yes
leaves named vulnerable to
replay attacks.

querylog

Specify whether query logging should be started when named
starts.
If querylog is not specified,
then the query logging
is determined by the presence of the logging category queries.

check-names

This option is used to restrict the character set and syntax
of
certain domain names in master files and/or DNS responses
received
from the network. The default varies according to usage
area. For
master zones the default is fail.
For slave zones the default
is warn.
For answers received from the network (response)
the default is ignore.

The rules for legal hostnames and mail domains are derived
from RFC 952 and RFC 821 as modified by RFC 1123.

check-names
applies to the owner names of A, AAAA and MX records.
It also applies to the domain names in the RDATA of NS, SOA,
MX, and SRV records.
It also applies to the RDATA of PTR records where the owner
name indicated that it is a reverse lookup of a hostname
(the owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).

check-dup-records

Check master zones for records that are treated as different
by DNSSEC but are semantically equal in plain DNS. The
default is to warn. Other possible
values are fail and
ignore.

check-mx

Check whether the MX record appears to refer to a IP address.
The default is to warn. Other possible
values are fail and
ignore.

check-wildcard

This option is used to check for non-terminal wildcards.
The use of non-terminal wildcards is almost always as a
result of a failure
to understand the wildcard matching algorithm (RFC 1034).
This option
affects master zones. The default (yes) is to check
for non-terminal wildcards and issue a warning.

check-integrity

Perform post load zone integrity checks on master
zones. This checks that MX and SRV records refer
to address (A or AAAA) records and that glue
address records exist for delegated zones. For
MX and SRV records only in-zone hostnames are
checked (for out-of-zone hostnames use
named-checkzone).
For NS records only names below top of zone are
checked (for out-of-zone names and glue consistency
checks use named-checkzone).
The default is yes.

The use of the SPF record for publishing Sender
Policy Framework is deprecated as the migration
from using TXT records to SPF records was abandoned.
Enabling this option also checks that a TXT Sender
Policy Framework record exists (starts with "v=spf1")
if there is an SPF record. Warnings are emitted if the
TXT record does not exist and can be suppressed with
check-spf.

check-mx-cname

If check-integrity is set then
fail, warn or ignore MX records that refer
to CNAMES. The default is to warn.

check-srv-cname

If check-integrity is set then
fail, warn or ignore SRV records that refer
to CNAMES. The default is to warn.

check-sibling

When performing integrity checks, also check that
sibling glue exists. The default is yes.

check-spf

If check-integrity is set then
check that there is a TXT Sender Policy Framework
record present (starts with "v=spf1") if there is an
SPF record present. The default is
warn.

zero-no-soa-ttl

When returning authoritative negative responses to
SOA queries set the TTL of the SOA record returned in
the authority section to zero.
The default is yes.

zero-no-soa-ttl-cache

When caching a negative response to a SOA query
set the TTL to zero.
The default is no.

update-check-ksk

When set to the default value of yes,
check the KSK bit in each key to determine how the key
should be used when generating RRSIGs for a secure zone.

Ordinarily, zone-signing keys (that is, keys without the
KSK bit set) are used to sign the entire zone, while
key-signing keys (keys with the KSK bit set) are only
used to sign the DNSKEY RRset at the zone apex.
However, if this option is set to no,
then the KSK bit is ignored; KSKs are treated as if they
were ZSKs and are used to sign the entire zone. This is
similar to the dnssec-signzone -z
command line option.

When this option is set to yes, there
must be at least two active keys for every algorithm
represented in the DNSKEY RRset: at least one KSK and one
ZSK per algorithm. If there is any algorithm for which
this requirement is not met, this option will be ignored
for that algorithm.

dnssec-dnskey-kskonly

When this option and update-check-ksk
are both set to yes, only key-signing
keys (that is, keys with the KSK bit set) will be used
to sign the DNSKEY RRset at the zone apex. Zone-signing
keys (keys without the KSK bit set) will be used to sign
the remainder of the zone, but not the DNSKEY RRset.
This is similar to the
dnssec-signzone -x command line option.

The default is no. If
update-check-ksk is set to
no, this option is ignored.

try-tcp-refresh

Try to refresh the zone using TCP if UDP queries fail.
For BIND 8 compatibility, the default is
yes.

dnssec-secure-to-insecure

Allow a dynamic zone to transition from secure to
insecure (i.e., signed to unsigned) by deleting all
of the DNSKEY records. The default is no.
If set to yes, and if the DNSKEY RRset
at the zone apex is deleted, all RRSIG and NSEC records
will be removed from the zone as well.

If the zone uses NSEC3, then it is also necessary to
delete the NSEC3PARAM RRset from the zone apex; this will
cause the removal of all corresponding NSEC3 records.
(It is expected that this requirement will be eliminated
in a future release.)

Note that if a zone has been configured with
auto-dnssec maintain and the
private keys remain accessible in the key repository,
then the zone will be automatically signed again the
next time named is started.

Forwarding

The forwarding facility can be used to create a large site-wide
cache on a few servers, reducing traffic over links to external
name servers. It can also be used to allow queries by servers that
do not have direct access to the Internet, but wish to look up
exterior
names anyway. Forwarding occurs only on those queries for which
the server is not authoritative and does not have the answer in
its cache.

forward

This option is only meaningful if the
forwarders list is not empty. A value of first,
the default, causes the server to query the forwarders
first — and
if that doesn't answer the question, the server will then
look for
the answer itself. If only is
specified, the
server will only query the forwarders.

forwarders

Specifies the IP addresses to be used
for forwarding. The default is the empty list (no
forwarding).

Forwarding can also be configured on a per-domain basis, allowing
for the global forwarding options to be overridden in a variety
of ways. You can set particular domains to use different
forwarders,
or have a different forward only/first behavior,
or not forward at all, see the section called “zone
Statement Grammar”.

Dual-stack Servers

Dual-stack servers are used as servers of last resort to work
around
problems in reachability due the lack of support for either IPv4
or IPv6
on the host machine.

dual-stack-servers

Specifies host names or addresses of machines with access to
both IPv4 and IPv6 transports. If a hostname is used, the
server must be able
to resolve the name using only the transport it has. If the
machine is dual
stacked, then the dual-stack-servers have no effect unless
access to a transport has been disabled on the command line
(e.g. named -4).

Access Control

Specifies which hosts are allowed to
notify this server, a slave, of zone changes in addition
to the zone masters.
allow-notify may also be
specified in the
zone statement, in which case
it overrides the
options allow-notify
statement. It is only meaningful
for a slave zone. If not specified, the default is to
process notify messages
only from a zone's master.

allow-query

Specifies which hosts are allowed to ask ordinary
DNS questions. allow-query may
also be specified in the zone
statement, in which case it overrides the
options allow-query statement.
If not specified, the default is to allow queries
from all hosts.

Note

allow-query-cache is now
used to specify access to the cache.

allow-query-on

Specifies which local addresses can accept ordinary
DNS questions. This makes it possible, for instance,
to allow queries on internal-facing interfaces but
disallow them on external-facing ones, without
necessarily knowing the internal network's addresses.

Note that allow-query-on is only
checked for queries that are permitted by
allow-query. A query must be
allowed by both ACLs, or it will be refused.

allow-query-on may
also be specified in the zone
statement, in which case it overrides the
options allow-query-on statement.

If not specified, the default is to allow queries
on all addresses.

Note

allow-query-cache is
used to specify access to the cache.

allow-query-cache

Specifies which hosts are allowed to get answers
from the cache. If allow-query-cache
is not set then allow-recursion
is used if set, otherwise allow-query
is used if set unless recursion no; is
set in which case none; is used,
otherwise the default (localnets;localhost;) is used.

allow-query-cache-on

Specifies which local addresses can give answers
from the cache. If not specified, the default is
to allow cache queries on any address,
localnets and
localhost.

allow-recursion

Specifies which hosts are allowed to make recursive
queries through this server. If
allow-recursion is not set
then allow-query-cache is
used if set, otherwise allow-query
is used if set, otherwise the default
(localnets;localhost;) is used.

allow-recursion-on

Specifies which local addresses can accept recursive
queries. If not specified, the default is to allow
recursive queries on all addresses.

allow-update

Specifies which hosts are allowed to
submit Dynamic DNS updates for master zones. The default is
to deny
updates from all hosts. Note that allowing updates based
on the requestor's IP address is insecure; see
the section called “Dynamic Update Security” for details.

allow-update-forwarding

Specifies which hosts are allowed to
submit Dynamic DNS updates to slave zones to be forwarded to
the
master. The default is { none; },
which
means that no update forwarding will be performed. To
enable
update forwarding, specify
allow-update-forwarding { any; };.
Specifying values other than { none; } or
{ any; } is usually
counterproductive, since
the responsibility for update access control should rest
with the
master server, not the slaves.

Note that enabling the update forwarding feature on a slave
server
may expose master servers relying on insecure IP address
based
access control to attacks; see the section called “Dynamic Update Security”
for more details.

allow-v6-synthesis

This option was introduced for the smooth transition from
AAAA
to A6 and from "nibble labels" to binary labels.
However, since both A6 and binary labels were then
deprecated,
this option was also deprecated.
It is now ignored with some warning messages.

allow-transfer

Specifies which hosts are allowed to
receive zone transfers from the server. allow-transfer may
also be specified in the zone
statement, in which
case it overrides the options allow-transfer statement.
If not specified, the default is to allow transfers to all
hosts.

blackhole

Specifies a list of addresses that the
server will not accept queries from or use to resolve a
query. Queries
from these addresses will not be responded to. The default
is none.

filter-aaaa

Specifies a list of addresses to which
filter-aaaa-on-v4
is applies. The default is any.

no-case-compress

Specifies a list of addresses which require responses
to use case-insensitive compression. This ACL can be
used when named needs to work with
clients that do not comply with the requirement in RFC
1034 to use case-insensitive name comparisons when
checking for matching domain names.

If left undefined, the ACL defaults to
none: case-insensitive compression
will be used for all clients. If the ACL is defined and
matches a client, then case will be ignored when
compressing domain names in DNS responses sent to that
client.

This can result in slightly smaller responses: if
a response contains the names "example.com" and
"example.COM", case-insensitive compression would treat
the second one as a duplicate. It also ensures
that the case of the query name exactly matches the
case of the owner names of returned records, rather
than matching the case of the records entered in
the zone file. This allows responses to exactly
match the query, which is required by some clients
due to incorrect use of case-sensitive comparisons.

Case-insensitive compression is always
used in AXFR and IXFR responses, regardless of whether
the client matches this ACL.

There are circumstances in which named
will not preserve the case of owner names of records:
if a zone file defines records of different types with
the same name, but the capitalization of the name is
different (e.g., "www.example.com/A" and
"WWW.EXAMPLE.COM/AAAA"), then all responses for that
name will use the first version
of the name that was used in the zone file. This
limitation may be addressed in a future release. However,
domain names specified in the rdata of resource records
(i.e., records of type NS, MX, CNAME, etc) will always
have their case preserved unless the client matches this
ACL.

resolver-query-timeout

The amount of time the resolver will spend attempting
to resolve a recursive query before failing. The default
and minimum is 10 and the maximum is
30. Setting it to 0
will result in the default being used.

Interfaces

The interfaces and ports that the server will answer queries
from may be specified using the listen-on option. listen-on takes
an optional port and an address_match_list
of IPv4 addresses. (IPv6 addresses are ignored, with a
logged warning.)
The server will listen on all interfaces allowed by the address
match list. If a port is not specified, port 53 will be used.

Multiple listen-on statements are
allowed.
For example,

listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };

will enable the name server on port 53 for the IP address
5.6.7.8, and on port 1234 of an address on the machine in net
1.2 that is not 1.2.3.4.

If no listen-on is specified, the
server will listen on port 53 on all IPv4 interfaces.

The listen-on-v6 option is used to
specify the interfaces and the ports on which the server will
listen
for incoming queries sent using IPv6.

When

{ any; }

is
specified
as the address_match_list for the
listen-on-v6 option,
the server does not bind a separate socket to each IPv6 interface
address as it does for IPv4 if the operating system has enough API
support for IPv6 (specifically if it conforms to RFC 3493 and RFC
3542).
Instead, it listens on the IPv6 wildcard address.
If the system only has incomplete API support for IPv6, however,
the behavior is the same as that for IPv4.

A list of particular IPv6 addresses can also be specified, in
which case
the server listens on a separate socket for each specified
address,
regardless of whether the desired API is supported by the system.
IPv4 addresses specified in listen-on-v6
will be ignored, with a logged warning.

will enable the name server on port 53 for any IPv6 addresses
(with a single wildcard socket),
and on port 1234 of IPv6 addresses that is not in the prefix
2001:db8::/32 (with separate sockets for each matched address.)

To make the server not listen on any IPv6 address, use

listen-on-v6 { none; };

If no listen-on-v6 option is
specified, the server will not listen on any IPv6 address
unless -6 is specified when named is
invoked. If -6 is specified then
named will listen on port 53 on all IPv6 interfaces by default.

Query Address

If the server doesn't know the answer to a question, it will
query other name servers. query-source specifies
the address and port used for such queries. For queries sent over
IPv6, there is a separate query-source-v6 option.
If address is * (asterisk) or is omitted,
a wildcard IP address (INADDR_ANY)
will be used.

If port is * or is omitted,
a random port number from a pre-configured
range is picked up and will be used for each query.
The port range(s) is that specified in
the use-v4-udp-ports (for IPv4)
and use-v6-udp-ports (for IPv6)
options, excluding the ranges specified in
the avoid-v4-udp-ports
and avoid-v6-udp-ports options, respectively.

The defaults of the query-source and
query-source-v6 options
are:

query-source address * port *;
query-source-v6 address * port *;

If use-v4-udp-ports or
use-v6-udp-ports is unspecified,
named will check if the operating
system provides a programming interface to retrieve the
system's default range for ephemeral ports.
If such an interface is available,
named will use the corresponding system
default range; otherwise, it will use its own defaults:

Note: make sure the ranges be sufficiently large for
security. A desirable size depends on various parameters,
but we generally recommend it contain at least 16384 ports
(14 bits of entropy).
Note also that the system's default range when used may be
too small for this purpose, and that the range may even be
changed while named is running; the new
range will automatically be applied when named
is reloaded.
It is encouraged to
configure use-v4-udp-ports and
use-v6-udp-ports explicitly so that the
ranges are sufficiently large and are reasonably
independent from the ranges used by other applications.

Note: the operational configuration
where named runs may prohibit the use
of some ports. For example, UNIX systems will not allow
named running without a root privilege
to use ports less than 1024.
If such ports are included in the specified (or detected)
set of query ports, the corresponding query attempts will
fail, resulting in resolution failures or delay.
It is therefore important to configure the set of ports
that can be safely used in the expected operational environment.

The defaults of the avoid-v4-udp-ports and
avoid-v6-udp-ports options
are:

avoid-v4-udp-ports {};
avoid-v6-udp-ports {};

Note: BIND 9.5.0 introduced
the use-queryport-pool
option to support a pool of such random ports, but this
option is now obsolete because reusing the same ports in
the pool may not be sufficiently secure.
For the same reason, it is generally strongly discouraged to
specify a particular port for the
query-source or
query-source-v6 options;
it implicitly disables the use of randomized port numbers.

use-queryport-pool

This option is obsolete.

queryport-pool-ports

This option is obsolete.

queryport-pool-updateinterval

This option is obsolete.

Note

The address specified in the query-source option
is used for both UDP and TCP queries, but the port applies only
to UDP queries. TCP queries always use a random
unprivileged port.

Note

Solaris 2.5.1 and earlier does not support setting the source
address for TCP sockets.

Note

See also transfer-source and
notify-source.

Zone Transfers

BIND has mechanisms in place to
facilitate zone transfers
and set limits on the amount of load that transfers place on the
system. The following options apply to zone transfers.

also-notify

Defines a global list of IP addresses of name servers
that are also sent NOTIFY messages whenever a fresh copy of
the
zone is loaded, in addition to the servers listed in the
zone's NS records.
This helps to ensure that copies of the zones will
quickly converge on stealth servers.
Optionally, a port may be specified with each
also-notify address to send
the notify messages to a port other than the
default of 53.
If an also-notify list
is given in a zone statement,
it will override
the options also-notify
statement. When a zone notify
statement
is set to no, the IP
addresses in the global also-notify list will
not be sent NOTIFY messages for that zone. The default is
the empty
list (no global notification list).

max-transfer-time-in

Inbound zone transfers running longer than
this many minutes will be terminated. The default is 120
minutes
(2 hours). The maximum value is 28 days (40320 minutes).

max-transfer-idle-in

Inbound zone transfers making no progress
in this many minutes will be terminated. The default is 60
minutes
(1 hour). The maximum value is 28 days (40320 minutes).

max-transfer-time-out

Outbound zone transfers running longer than
this many minutes will be terminated. The default is 120
minutes
(2 hours). The maximum value is 28 days (40320 minutes).

max-transfer-idle-out

Outbound zone transfers making no progress
in this many minutes will be terminated. The default is 60
minutes (1
hour). The maximum value is 28 days (40320 minutes).

serial-query-rate

Slave servers will periodically query master
servers to find out if zone serial numbers have
changed. Each such query uses a minute amount of
the slave server's network bandwidth. To limit
the amount of bandwidth used, BIND 9 limits the
rate at which queries are sent. The value of the
serial-query-rate option, an
integer, is the maximum number of queries sent
per second. The default is 20.

In addition to controlling the rate SOA refresh
queries are issued at
serial-query-rate also controls
the rate at which NOTIFY messages are sent from
both master and slave zones.

serial-queries

In BIND 8, the serial-queries
option
set the maximum number of concurrent serial number queries
allowed to be outstanding at any given time.
BIND 9 does not limit the number of outstanding
serial queries and ignores the serial-queries option.
Instead, it limits the rate at which the queries are sent
as defined using the serial-query-rate option.

transfer-format

Zone transfers can be sent using two different formats,
one-answer and
many-answers.
The transfer-format option is used
on the master server to determine which format it sends.
one-answer uses one DNS message per
resource record transferred.
many-answers packs as many resource
records as possible into a message.
many-answers is more efficient, but is
only supported by relatively new slave servers,
such as BIND 9, BIND
8.x and BIND 4.9.5 onwards.
The many-answers format is also supported by
recent Microsoft Windows nameservers.
The default is many-answers.
transfer-format may be overridden on a
per-server basis by using the server
statement.

transfers-in

The maximum number of inbound zone transfers
that can be running concurrently. The default value is 10.
Increasing transfers-in may
speed up the convergence
of slave zones, but it also may increase the load on the
local system.

transfers-out

The maximum number of outbound zone transfers
that can be running concurrently. Zone transfer requests in
excess
of the limit will be refused. The default value is 10.

transfers-per-ns

The maximum number of inbound zone transfers
that can be concurrently transferring from a given remote
name server.
The default value is 2.
Increasing transfers-per-ns
may
speed up the convergence of slave zones, but it also may
increase
the load on the remote name server. transfers-per-ns may
be overridden on a per-server basis by using the transfers phrase
of the server statement.

transfer-source

transfer-source
determines which local address will be bound to IPv4
TCP connections used to fetch zones transferred
inbound by the server. It also determines the
source IPv4 address, and optionally the UDP port,
used for the refresh queries and forwarded dynamic
updates. If not set, it defaults to a system
controlled value which will usually be the address
of the interface "closest to" the remote end. This
address must appear in the remote end's
allow-transfer option for the
zone being transferred, if one is specified. This
statement sets the
transfer-source for all zones,
but can be overridden on a per-view or per-zone
basis by including a
transfer-source statement within
the view or
zone block in the configuration
file.

Note

Solaris 2.5.1 and earlier does not support setting the
source address for TCP sockets.

transfer-source-v6

The same as transfer-source,
except zone transfers are performed using IPv6.

alt-transfer-source

An alternate transfer source if the one listed in
transfer-source fails and
use-alt-transfer-source is
set.

Note

If you do not wish the alternate transfer source
to be used, you should set
use-alt-transfer-source
appropriately and you should not depend upon
getting an answer back to the first refresh
query.

alt-transfer-source-v6

An alternate transfer source if the one listed in
transfer-source-v6 fails and
use-alt-transfer-source is
set.

use-alt-transfer-source

Use the alternate transfer sources or not. If views are
specified this defaults to no
otherwise it defaults to
yes (for BIND 8
compatibility).

notify-source

notify-source
determines which local source address, and
optionally UDP port, will be used to send NOTIFY
messages. This address must appear in the slave
server's masters zone clause or
in an allow-notify clause. This
statement sets the notify-source
for all zones, but can be overridden on a per-zone or
per-view basis by including a
notify-source statement within
the zone or
view block in the configuration
file.

Note

Solaris 2.5.1 and earlier does not support setting the
source address for TCP sockets.

notify-source-v6

Like notify-source,
but applies to notify messages sent to IPv6 addresses.

UDP Port Lists

use-v4-udp-ports,
avoid-v4-udp-ports,
use-v6-udp-ports, and
avoid-v6-udp-ports
specify a list of IPv4 and IPv6 UDP ports that will be
used or not used as source ports for UDP messages.
See the section called “Query Address” about how the
available ports are determined.
For example, with the following configuration

UDP ports of IPv6 messages sent
from named will be in one
of the following ranges: 32768 to 39999, 40001 to 49999,
and 60001 to 65535.

avoid-v4-udp-ports and
avoid-v6-udp-ports can be used
to prevent named from choosing as its random source port a
port that is blocked by your firewall or a port that is
used by other applications;
if a query went out with a source port blocked by a
firewall, the
answer would not get by the firewall and the name server would
have to query again.
Note: the desired range can also be represented only with
use-v4-udp-ports and
use-v6-udp-ports, and the
avoid- options are redundant in that
sense; they are provided for backward compatibility and
to possibly simplify the port specification.

Operating System Resource Limits

The server's usage of many system resources can be limited.
Scaled values are allowed when specifying resource limits. For
example, 1G can be used instead of
1073741824 to specify a limit of
one
gigabyte. unlimited requests
unlimited use, or the
maximum available amount. default
uses the limit
that was in force when the server was started. See the description
of size_spec in the section called “Configuration File Elements”.

The following options set operating system resource limits for
the name server process. Some operating systems don't support
some or
any of the limits. On such systems, a warning will be issued if
the
unsupported limit is used.

coresize

The maximum size of a core dump. The default
is default.

datasize

The maximum amount of data memory the server
may use. The default is default.
This is a hard limit on server memory usage.
If the server attempts to allocate memory in excess of this
limit, the allocation will fail, which may in turn leave
the server unable to perform DNS service. Therefore,
this option is rarely useful as a way of limiting the
amount of memory used by the server, but it can be used
to raise an operating system data size limit that is
too small by default. If you wish to limit the amount
of memory used by the server, use the
max-cache-size and
recursive-clients
options instead.

files

The maximum number of files the server
may have open concurrently. The default is unlimited.

stacksize

The maximum amount of stack memory the server
may use. The default is default.

Server Resource Limits

The following options set limits on the server's
resource consumption that are enforced internally by the
server rather than the operating system.

max-ixfr-log-size

This option is obsolete; it is accepted
and ignored for BIND 8 compatibility. The option
max-journal-size performs a
similar function in BIND 9.

max-journal-size

Sets a maximum size for each journal file
(see the section called “The journal file”). When the journal file
approaches
the specified size, some of the oldest transactions in the
journal
will be automatically removed. The default is
unlimited.
This may also be set on a per-zone basis.

host-statistics-max

In BIND 8, specifies the maximum number of host statistics
entries to be kept.
Not implemented in BIND 9.

recursive-clients

The maximum number of simultaneous recursive lookups
the server will perform on behalf of clients. The default
is
1000. Because each recursing
client uses a fair
bit of memory, on the order of 20 kilobytes, the value of
the
recursive-clients option may
have to be decreased
on hosts with limited memory.

tcp-clients

The maximum number of simultaneous client TCP
connections that the server will accept.
The default is 100.

reserved-sockets

The number of file descriptors reserved for TCP, stdio,
etc. This needs to be big enough to cover the number of
interfaces named listens on, tcp-clients as well as
to provide room for outgoing TCP queries and incoming zone
transfers. The default is 512.
The minimum value is 128 and the
maximum value is 128 less than
maxsockets (-S). This option may be removed in the future.

This option has little effect on Windows.

max-cache-size

The maximum amount of memory to use for the
server's cache, in bytes.
When the amount of data in the cache
reaches this limit, the server will cause records to expire
prematurely based on an LRU based strategy so that
the limit is not exceeded.
A value of 0 is special, meaning that
records are purged from the cache only when their
TTLs expire.
Another special keyword unlimited
means the maximum value of 32-bit unsigned integers
(0xffffffff), which may not have the same effect as
0 on machines that support more than 32 bits of
memory space.
Any positive values less than 2MB will be ignored reset
to 2MB.
In a server with multiple views, the limit applies
separately to the cache of each view.
The default is 0.

tcp-listen-queue

The listen queue depth. The default and minimum is 10.
If the kernel supports the accept filter "dataready" this
also controls how
many TCP connections that will be queued in kernel space
waiting for
some data before being passed to accept. Nonzero values
less than 10 will be silently raised. A value of 0 may also
be used; on most platforms this sets the listen queue
length to a system-defined default value.

Periodic Task Intervals

cleaning-interval

This interval is effectively obsolete. Previously,
the server would remove expired resource records
from the cache every cleaning-interval minutes.
BIND 9 now manages cache
memory in a more sophisticated manner and does not
rely on the periodic cleaning any more.
Specifying this option therefore has no effect on
the server's behavior.

heartbeat-interval

The server will perform zone maintenance tasks
for all zones marked as dialup whenever this
interval expires. The default is 60 minutes. Reasonable
values are up
to 1 day (1440 minutes). The maximum value is 28 days
(40320 minutes).
If set to 0, no zone maintenance for these zones will occur.

interface-interval

The server will scan the network interface list
every interface-interval
minutes. The default
is 60 minutes. The maximum value is 28 days (40320 minutes).
If set to 0, interface scanning will only occur when
the configuration file is loaded. After the scan, the
server will
begin listening for queries on any newly discovered
interfaces (provided they are allowed by the
listen-on configuration), and
will
stop listening on interfaces that have gone away.

statistics-interval

Name server statistics will be logged
every statistics-interval
minutes. The default is
60. The maximum value is 28 days (40320 minutes).
If set to 0, no statistics will be logged.

Note

Not yet implemented in
BIND 9.

Topology

All other things being equal, when the server chooses a name
server
to query from a list of name servers, it prefers the one that is
topologically closest to itself. The topology statement
takes an address_match_list and
interprets it
in a special way. Each top-level list element is assigned a
distance.
Non-negated elements get a distance based on their position in the
list, where the closer the match is to the start of the list, the
shorter the distance is between it and the server. A negated match
will be assigned the maximum distance from the server. If there
is no match, the address will get a distance which is further than
any non-negated list element, and closer than any negated element.
For example,

topology {
10/8;
!1.2.3/24;
{ 1.2/16; 3/8; };
};

will prefer servers on network 10 the most, followed by hosts
on network 1.2.0.0 (netmask 255.255.0.0) and network 3, with the
exception of hosts on network 1.2.3 (netmask 255.255.255.0), which
is preferred least of all.

The default topology is

topology { localhost; localnets; };

Note

The topology option
is not implemented in BIND 9.

The sortlist Statement

The response to a DNS query may consist of multiple resource
records (RRs) forming a resource records set (RRset).
The name server will normally return the
RRs within the RRset in an indeterminate order
(but see the rrset-order
statement in the section called “RRset Ordering”).
The client resolver code should rearrange the RRs as appropriate,
that is, using any addresses on the local net in preference to
other addresses.
However, not all resolvers can do this or are correctly
configured.
When a client is using a local server, the sorting can be performed
in the server, based on the client's address. This only requires
configuring the name servers, not all the clients.

The sortlist statement (see below)
takes
an address_match_list and
interprets it even
more specifically than the topology
statement
does (the section called “Topology”).
Each top level statement in the sortlist must
itself be an explicit address_match_list with
one or two elements. The first element (which may be an IP
address,
an IP prefix, an ACL name or a nested address_match_list)
of each top level list is checked against the source address of
the query until a match is found.

Once the source address of the query has been matched, if
the top level statement contains only one element, the actual
primitive
element that matched the source address is used to select the
address
in the response to move to the beginning of the response. If the
statement is a list of two elements, then the second element is
treated the same as the address_match_list in
a topology statement. Each top
level element
is assigned a distance and the address in the response with the
minimum
distance is moved to the beginning of the response.

In the following example, any queries received from any of
the addresses of the host itself will get responses preferring
addresses
on any of the locally connected networks. Next most preferred are
addresses
on the 192.168.1/24 network, and after that either the
192.168.2/24
or
192.168.3/24 network with no preference shown between these two
networks. Queries received from a host on the 192.168.1/24 network
will prefer other addresses on that network to the 192.168.2/24
and
192.168.3/24 networks. Queries received from a host on the
192.168.4/24
or the 192.168.5/24 network will only prefer other addresses on
their directly connected networks.

The following example will give reasonable behavior for the
local host and hosts on directly connected networks. It is similar
to the behavior of the address sort in BIND 4.9.x. Responses sent
to queries from the local host will favor any of the directly
connected
networks. Responses sent to queries from any other hosts on a
directly
connected network will prefer addresses on that same network.
Responses
to other queries will not be sorted.

sortlist {
{ localhost; localnets; };
{ localnets; };
};

RRset Ordering

When multiple records are returned in an answer it may be
useful to configure the order of the records placed into the
response.
The rrset-order statement permits
configuration
of the ordering of the records in a multiple record response.
See also the sortlist statement,
the section called “The sortlist Statement”.

If no class is specified, the default is ANY.
If no type is specified, the default is ANY.
If no name is specified, the default is "*" (asterisk).

The legal values for ordering are:

fixed

Records are returned in the order they
are defined in the zone file.

random

Records are returned in some random order.

cyclic

Records are returned in a cyclic round-robin order.

If BIND is configured with the
"--enable-fixed-rrset" option at compile time, then
the initial ordering of the RRset will match the
one specified in the zone file.

For example:

rrset-order {
class IN type A name "host.example.com" order random;
order cyclic;
};

will cause any responses for type A records in class IN that
have "host.example.com" as a
suffix, to always be returned
in random order. All other records are returned in cyclic order.

If multiple rrset-order statements
appear,
they are not combined — the last one applies.

Note

In this release of BIND 9, the
rrset-order statement does not support
"fixed" ordering by default. Fixed ordering can be enabled
at compile time by specifying "--enable-fixed-rrset" on
the "configure" command line.

Tuning

lame-ttl

Sets the number of seconds to cache a
lame server indication. 0 disables caching. (This is
NOT recommended.)
The default is 600 (10 minutes) and the
maximum value is
1800 (30 minutes).

Lame-ttl also controls the amount of time DNSSEC
validation failures are cached. There is a minimum
of 30 seconds applied to bad cache entries if the
lame-ttl is set to less than 30 seconds.

max-ncache-ttl

To reduce network traffic and increase performance,
the server stores negative answers. max-ncache-ttl is
used to set a maximum retention time for these answers in
the server
in seconds. The default
max-ncache-ttl is 10800 seconds (3 hours).
max-ncache-ttl cannot exceed
7 days and will
be silently truncated to 7 days if set to a greater value.

max-cache-ttl

Sets the maximum time for which the server will
cache ordinary (positive) answers. The default is
one week (7 days).
A value of zero may cause all queries to return
SERVFAIL, because of lost caches of intermediate
RRsets (such as NS and glue AAAA/A records) in the
resolution process.

min-roots

The minimum number of root servers that
is required for a request for the root servers to be
accepted. The default
is 2.

Note

Not implemented in BIND 9.

sig-validity-interval

Specifies the number of days into the future when
DNSSEC signatures automatically generated as a
result of dynamic updates (the section called “Dynamic Update”) will expire. There
is an optional second field which specifies how
long before expiry that the signatures will be
regenerated. If not specified, the signatures will
be regenerated at 1/4 of base interval. The second
field is specified in days if the base interval is
greater than 7 days otherwise it is specified in hours.
The default base interval is 30 days
giving a re-signing interval of 7 1/2 days. The maximum
values are 10 years (3660 days).

The signature inception time is unconditionally
set to one hour before the current time to allow
for a limited amount of clock skew.

The sig-validity-interval
should be, at least, several multiples of the SOA
expire interval to allow for reasonable interaction
between the various timer and expiry dates.

sig-signing-nodes

Specify the maximum number of nodes to be
examined in each quantum when signing a zone with
a new DNSKEY. The default is
100.

sig-signing-signatures

Specify a threshold number of signatures that
will terminate processing a quantum when signing
a zone with a new DNSKEY. The default is
10.

sig-signing-type

Specify a private RDATA type to be used when generating
key signing records. The default is
65534.

It is expected that this parameter may be removed
in a future version once there is a standard type.

min-refresh-time, max-refresh-time, min-retry-time, max-retry-time

These options control the server's behavior on refreshing a
zone
(querying for SOA changes) or retrying failed transfers.
Usually the SOA values for the zone are used, but these
values
are set by the master, giving slave server administrators
little
control over their contents.

These options allow the administrator to set a minimum and
maximum
refresh and retry time either per-zone, per-view, or
globally.
These options are valid for slave and stub zones,
and clamp the SOA refresh and retry times to the specified
values.

Sets the advertised EDNS UDP buffer size in bytes
to control the size of packets received.
Valid values are 512 to 4096 (values outside this range
will be silently adjusted). The default value
is 4096. The usual reason for setting
edns-udp-size to a non-default
value is to get UDP answers to pass through broken
firewalls that block fragmented packets and/or
block UDP packets that are greater than 512 bytes.

named will fallback to using 512 bytes
if it get a series of timeout at the initial value. 512
bytes is not being offered to encourage sites to fix their
firewalls. Small EDNS UDP sizes will result in the
excessive use of TCP.

max-udp-size

Sets the maximum EDNS UDP message size
named will send in bytes.
Valid values are 512 to 4096 (values outside this
range will be silently adjusted). The default
value is 4096. The usual reason for setting
max-udp-size to a non-default
value is to get UDP answers to pass through broken
firewalls that block fragmented packets and/or
block UDP packets that are greater than 512 bytes.
This is independent of the advertised receive
buffer (edns-udp-size).

Setting this to a low value will encourage additional
TCP traffic to the nameserver.

masterfile-format

Specifies
the file format of zone files (see
the section called “Additional File Formats”).
The default value is text, which is the
standard textual representation. Files in other formats
than text are typically expected
to be generated by the named-compilezone tool.
Note that when a zone file in a different format than
text is loaded, named
may omit some of the checks which would be performed for a
file in the text format. In particular,
check-names checks do not apply
for the raw format. This means
a zone file in the raw format
must be generated with the same check level as that
specified in the named configuration
file. This statement sets the
masterfile-format for all zones,
but can be overridden on a per-zone or per-view basis
by including a masterfile-format
statement within the zone or
view block in the configuration
file.

clients-per-query, max-clients-per-query

These set the
initial value (minimum) and maximum number of recursive
simultaneous clients for any given query
(<qname,qtype,qclass>) that the server will accept
before dropping additional clients. named will attempt to
self tune this value and changes will be logged. The
default values are 10 and 100.

This value should reflect how many queries come in for
a given name in the time it takes to resolve that name.
If the number of queries exceed this value, named will
assume that it is dealing with a non-responsive zone
and will drop additional queries. If it gets a response
after dropping queries, it will raise the estimate. The
estimate will then be lowered in 20 minutes if it has
remained unchanged.

If clients-per-query is set to zero,
then there is no limit on the number of clients per query
and no queries will be dropped.

If max-clients-per-query is set to zero,
then there is no upper bound other than imposed by
recursive-clients.

notify-delay

The delay, in seconds, between sending sets of notify
messages for a zone. The default is five (5) seconds.

The overall rate that NOTIFY messages are sent for all
zones is controlled by serial-query-rate.

Built-in server information zones

The server provides some helpful diagnostic information
through a number of built-in zones under the
pseudo-top-level-domain bind in the
CHAOS class. These zones are part
of a
built-in view (see the section called “view Statement Grammar”) of
class
CHAOS which is separate from the
default view of class IN. Most global
configuration options (allow-query,
etc) will apply to this view, but some are locally
overridden: notify,
recursion and
allow-new-zones are
always set to no.

If you need to disable these zones, use the options
below, or hide the built-in CHAOS
view by
defining an explicit view of class CHAOS
that matches all clients.

version

The version the server should report
via a query of the name version.bind
with type TXT, class CHAOS.
The default is the real version number of this server.
Specifying version none
disables processing of the queries.

hostname

The hostname the server should report via a query of
the name hostname.bind
with type TXT, class CHAOS.
This defaults to the hostname of the machine hosting the
name server as
found by the gethostname() function. The primary purpose of such queries
is to
identify which of a group of anycast servers is actually
answering your queries. Specifying hostname none;
disables processing of the queries.

server-id

The ID the server should report when receiving a Name
Server Identifier (NSID) query, or a query of the name
ID.SERVER with type
TXT, class CHAOS.
The primary purpose of such queries is to
identify which of a group of anycast servers is actually
answering your queries. Specifying server-id none;
disables processing of the queries.
Specifying server-id hostname; will cause named to
use the hostname as found by the gethostname() function.
The default server-id is none.

Built-in Empty Zones

Named has some built-in empty zones (SOA and NS records only).
These are for zones that should normally be answered locally
and which queries should not be sent to the Internet's root
servers. The official servers which cover these namespaces
return NXDOMAIN responses to these queries. In particular,
these cover the reverse namespaces for addresses from
RFC 1918, RFC 4193, RFC 5737 and RFC 6598. They also include the
reverse namespace for IPv6 local address (locally assigned),
IPv6 link local addresses, the IPv6 loopback address and the
IPv6 unknown address.

Named will attempt to determine if a built-in zone already exists
or is active (covered by a forward-only forwarding declaration)
and will not create an empty zone in that case.

Empty zones are settable at the view level and only apply to
views of class IN. Disabled empty zones are only inherited
from options if there are no disabled empty zones specified
at the view level. To override the options list of disabled
zones, you can disable the root zone at the view level, for example:

disable-empty-zone ".";

If you are using the address ranges covered here, you should
already have reverse zones covering the addresses you use.
In practice this appears to not be the case with many queries
being made to the infrastructure servers for names in these
spaces. So many in fact that sacrificial servers were needed
to be deployed to channel the query load away from the
infrastructure servers.

Note

The real parent servers for these zones should disable all
empty zone under the parent zone they serve. For the real
root servers, this is all built-in empty zones. This will
enable them to return referrals to deeper in the tree.

empty-server

Specify what server name will appear in the returned
SOA record for empty zones. If none is specified, then
the zone's name will be used.

empty-contact

Specify what contact name will appear in the returned
SOA record for empty zones. If none is specified, then
"." will be used.

empty-zones-enable

Enable or disable all empty zones. By default, they
are enabled.

disable-empty-zone

Disable individual empty zones. By default, none are
disabled. This option can be specified multiple times.

Additional Section Caching

The additional section cache, also called acache,
is an internal cache to improve the response performance of BIND 9.
When additional section caching is enabled, BIND 9 will
cache an internal short-cut to the additional section content for
each answer RR.
Note that acache is an internal caching
mechanism of BIND 9, and is not related to the DNS caching
server function.

Additional section caching does not change the
response content (except the RRsets ordering of the additional
section, see below), but can improve the response performance
significantly.
It is particularly effective when BIND 9 acts as an authoritative
server for a zone that has many delegations with many glue RRs.

In order to obtain the maximum performance improvement
from additional section caching, setting
additional-from-cache
to no is recommended, since the current
implementation of acache
does not short-cut of additional section information from the
DNS cache data.

One obvious disadvantage of acache is
that it requires much more
memory for the internal cached data.
Thus, if the response performance does not matter and memory
consumption is much more critical, the
acache mechanism can be
disabled by setting acache-enable to
no.
It is also possible to specify the upper limit of memory
consumption
for acache by using max-acache-size.

Additional section caching also has a minor effect on the
RRset ordering in the additional section.
Without acache,
cyclic order is effective for the additional
section as well as the answer and authority sections.
However, additional section caching fixes the ordering when it
first caches an RRset for the additional section, and the same
ordering will be kept in succeeding responses, regardless of the
setting of rrset-order.
The effect of this should be minor, however, since an
RRset in the additional section
typically only contains a small number of RRs (and in many cases
it only contains a single RR), in which case the
ordering does not matter much.

The following is a summary of options related to
acache.

acache-enable

If yes, additional section caching is
enabled. The default value is no.

acache-cleaning-interval

The server will remove stale cache entries, based on an LRU
based
algorithm, every acache-cleaning-interval minutes.
The default is 60 minutes.
If set to 0, no periodic cleaning will occur.

max-acache-size

The maximum amount of memory in bytes to use for the server's acache.
When the amount of data in the acache reaches this limit,
the server
will clean more aggressively so that the limit is not
exceeded.
In a server with multiple views, the limit applies
separately to the
acache of each view.
The default is 16M.

Content Filtering

BIND 9 provides the ability to filter
out DNS responses from external DNS servers containing
certain types of data in the answer section.
Specifically, it can reject address (A or AAAA) records if
the corresponding IPv4 or IPv6 addresses match the given
address_match_list of the
deny-answer-addresses option.
It can also reject CNAME or DNAME records if the "alias"
name (i.e., the CNAME alias or the substituted query name
due to DNAME) matches the
given namelist of the
deny-answer-aliases option, where
"match" means the alias name is a subdomain of one of
the name_list elements.
If the optional namelist is specified
with except-from, records whose query name
matches the list will be accepted regardless of the filter
setting.
Likewise, if the alias name is a subdomain of the
corresponding zone, the deny-answer-aliases
filter will not apply;
for example, even if "example.com" is specified for
deny-answer-aliases,

www.example.com. CNAME xxx.example.com.

returned by an "example.com" server will be accepted.

In the address_match_list of the
deny-answer-addresses option, only
ip_addr
and ip_prefix
are meaningful;
any key_id will be silently ignored.

If a response message is rejected due to the filtering,
the entire message is discarded without being cached, and
a SERVFAIL error will be returned to the client.

This filtering is intended to prevent "DNS rebinding attacks," in
which an attacker, in response to a query for a domain name the
attacker controls, returns an IP address within your own network or
an alias name within your own domain.
A naive web browser or script could then serve as an
unintended proxy, allowing the attacker
to get access to an internal node of your local network
that couldn't be externally accessed otherwise.
See the paper available at
http://portal.acm.org/citation.cfm?id=1315245.1315298
for more details about the attacks.

For example, if you own a domain named "example.net" and
your internal network uses an IPv4 prefix 192.0.2.0/24,
you might specify the following rules:

If an external attacker lets a web browser in your local
network look up an IPv4 address of "attacker.example.com",
the attacker's DNS server would return a response like this:

attacker.example.com. A 192.0.2.1

in the answer section.
Since the rdata of this record (the IPv4 address) matches
the specified prefix 192.0.2.0/24, this response will be
ignored.

On the other hand, if the browser looks up a legitimate
internal web server "www.example.net" and the
following response is returned to
the BIND 9 server

www.example.net. A 192.0.2.2

it will be accepted since the owner name "www.example.net"
matches the except-from element,
"example.net".

Note that this is not really an attack on the DNS per se.
In fact, there is nothing wrong for an "external" name to
be mapped to your "internal" IP address or domain name
from the DNS point of view.
It might actually be provided for a legitimate purpose,
such as for debugging.
As long as the mapping is provided by the correct owner,
it is not possible or does not make sense to detect
whether the intent of the mapping is legitimate or not
within the DNS.
The "rebinding" attack must primarily be protected at the
application that uses the DNS.
For a large site, however, it may be difficult to protect
all possible applications at once.
This filtering feature is provided only to help such an
operational environment;
it is generally discouraged to turn it on unless you are
very sure you have no other choice and the attack is a
real threat for your applications.

Care should be particularly taken if you want to use this
option for addresses within 127.0.0.0/8.
These addresses are obviously "internal", but many
applications conventionally rely on a DNS mapping from
some name to such an address.
Filtering out DNS records containing this address
spuriously can break such applications.

Response Policy Zone (RPZ) Rewriting

BIND 9 includes a limited
mechanism to modify DNS responses for requests
analogous to email anti-spam DNS blacklists.
Responses can be changed to deny the existence of domains(NXDOMAIN),
deny the existence of IP addresses for domains (NODATA),
or contain other IP addresses or data.

Response policy zones are named in the
response-policy option for the view or among the
global options if there is no response-policy option for the view.
RPZs are ordinary DNS zones containing RRsets
that can be queried normally if allowed.
It is usually best to restrict those queries with something like
allow-query { localhost; };.

Four policy triggers are encoded in RPZ records, QNAME, IP, NSIP,
and NSDNAME.
QNAME RPZ records triggered by query names of requests and targets
of CNAME records resolved to generate the response.
The owner name of a QNAME RPZ record is the query name relativized
to the RPZ.

The second kind of RPZ trigger is an IP address in an A and AAAA
record in the ANSWER section of a response.
IP address triggers are encoded in records that have owner names
that are subdomains of rpz-ip relativized
to the RPZ origin name and encode an IP address or address block.
IPv4 trigger addresses are represented as
prefixlength.B4.B3.B2.B1.rpz-ip.
The prefix length must be between 1 and 32.
All four bytes, B4, B3, B2, and B1, must be present.
B4 is the decimal value of the least significant byte of the
IPv4 address as in IN-ADDR.ARPA.
IPv6 addresses are encoded in a format similar to the standard
IPv6 text representation,
prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-ip.
Each of W8,...,W1 is a one to four digit hexadecimal number
representing 16 bits of the IPv6 address as in the standard text
representation of IPv6 addresses, but reversed as in IN-ADDR.ARPA.
All 8 words must be present except when consecutive
zero words are replaced with .zz.
analogous to double colons (::) in standard IPv6 text encodings.
The prefix length must be between 1 and 128.

NSDNAME triggers match names of authoritative servers
for the query name, a parent of the query name, a CNAME for
query name, or a parent of a CNAME.
They are encoded as subdomains of
rpz-nsdomain relativized
to the RPZ origin name.
NSIP triggers match IP addresses in A and
AAAA RRsets for domains that can be checked against NSDNAME
policy records.
NSIP triggers are encoded like IP triggers except as subdomains of
rpz-nsip.
NSDNAME and NSIP triggers are checked only for names with at
least min-ns-dots dots.
The default value of min-ns-dots is 1 to
exclude top level domains.

The query response is checked against all RPZs, so
two or more policy records can be triggered by a response.
Because DNS responses can be rewritten according to at most one
policy record, a single record encoding an action (other than
DISABLED actions) must be chosen.
Triggers or the records that encode them are chosen in
the following order:

Choose the triggered record in the zone that appears
first in the response-policy option.

Prefer QNAME to IP to NSDNAME to NSIP triggers
in a single zone.

Among NSDNAME triggers, prefer the
trigger that matches the smallest name under the DNSSEC ordering.

Among IP or NSIP triggers, prefer the trigger
with the longest prefix.

Among triggers with the same prefex length,
prefer the IP or NSIP trigger that matches
the smallest IP address.

When the processing of a response is restarted to resolve
DNAME or CNAME records and a policy record set has
not been triggered,
all RPZs are again consulted for the DNAME or CNAME names
and addresses.

RPZ record sets are sets of any types of DNS record except
DNAME or DNSSEC that encode actions or responses to queries.

The NXDOMAIN response is encoded
by a CNAME whose target is the root domain (.)

A CNAME whose target is the wildcard top-level
domain (*.) specifies the NODATA action,
which rewrites the response to NODATA or ANCOUNT=1.

The Local Data action is
represented by a set ordinary DNS records that are used
to answer queries. Queries for record types not the
set are answered with NODATA.
A special form of local data is a CNAME whose target is a
wildcard such as *.example.com.
It is used as if were an ordinary CNAME after the astrisk (*)
has been replaced with the query name.
The purpose for this special form is query logging in the
walled garden's authority DNS server.

The PASSTHRU policy is specified
by a CNAME whose target is rpz-passthru.
It causes the response to not be rewritten
and is most often used to "poke holes" in policies for
CIDR blocks.
(A CNAME whose target is the variable part of its owner name
is an obsolete specification of the PASSTHRU policy.)

The actions specified in an RPZ can be overridden with a
policy clause in the
response-policy option.
An organization using an RPZ provided by another organization might
use this mechanism to redirect domains to its own walled garden.

GIVEN says "do not override but
perform the action specified in the zone."

DISABLED causes policy records to do
nothing but log what they might have done.
The response to the DNS query will be written according to
any triggered policy records that are not disabled.
Disabled policy zones should appear first,
because they will often not be logged
if a higher precedence trigger is found first.

PASSTHRU causes all policy records
to act as if they were CNAME records with targets the variable
part of their owner name. They protect the response from
being changed.

NXDOMAIN causes all RPZ records
to specify NXDOMAIN policies.

NODATA overrides with the
NODATA policy

CNAME domain causes all RPZ
policy records to act as if they were "cname domain" records.

By default, the actions encoded in an RPZ are applied
only to queries that ask for recursion (RD=1).
That default can be changed for a single RPZ or all RPZs in a view
with a recursive-only no clause.
This feature is useful for serving the same zone files
both inside and outside an RFC 1918 cloud and using RPZ to
delete answers that would otherwise contain RFC 1918 values
on the externally visible name server or view.

Also by default, RPZ actions are applied only to DNS requests that
either do not request DNSSEC metadata (DO=0) or when no DNSSEC
records are available for request name in the original zone (not
the response policy zone).
This default can be changed for all RPZs in a view with a
break-dnssec yes clause.
In that case, RPZ actions are applied regardless of DNSSEC.
The name of the clause option reflects the fact that results
rewritten by RPZ actions cannot verify.

The TTL of a record modified by RPZ policies is set from the
TTL of the relevant record in policy zone. It is then limited
to a maximum value.
The max-policy-ttl clause changes that
maximum from its default of 5.

RPZ can affect server performance.
Each configured response policy zone requires the server to
perform one to four additional database lookups before a
query can be answered.
For example, a DNS server with four policy zones, each with all
four kinds of response triggers, QNAME, IP, NSIP, and
NSDNAME, requires a total of 17 times as many database
lookups as a similar DNS server with no response policy zones.
A BIND9 server with adequate memory and one
response policy zone with QNAME and IP triggers might achieve a
maximum queries-per-second rate about 20% lower.
A server with four response policy zones with QNAME and IP
triggers might have a maximum QPS rate about 50% lower.

server Statement Definition and
Usage

The server statement defines
characteristics
to be associated with a remote name server. If a prefix length is
specified, then a range of servers is covered. Only the most
specific
server clause applies regardless of the order in
named.conf.

The server statement can occur at
the top level of the
configuration file or inside a view
statement.
If a view statement contains
one or more server statements, only
those
apply to the view and any top-level ones are ignored.
If a view contains no server
statements,
any top-level server statements are
used as
defaults.

If you discover that a remote server is giving out bad data,
marking it as bogus will prevent further queries to it. The
default
value of bogus is no.

The provide-ixfr clause determines
whether
the local server, acting as master, will respond with an
incremental
zone transfer when the given remote server, a slave, requests it.
If set to yes, incremental transfer
will be provided
whenever possible. If set to no,
all transfers
to the remote server will be non-incremental. If not set, the
value
of the provide-ixfr option in the
view or
global options block is used as a default.

The request-ixfr clause determines
whether
the local server, acting as a slave, will request incremental zone
transfers from the given remote server, a master. If not set, the
value of the request-ixfr option in
the view or
global options block is used as a default.

IXFR requests to servers that do not support IXFR will
automatically
fall back to AXFR. Therefore, there is no need to manually list
which servers support IXFR and which ones do not; the global
default
of yes should always work.
The purpose of the provide-ixfr and
request-ixfr clauses is
to make it possible to disable the use of IXFR even when both
master
and slave claim to support it, for example if one of the servers
is buggy and crashes or corrupts data when IXFR is used.

The edns clause determines whether
the local server will attempt to use EDNS when communicating
with the remote server. The default is yes.

The edns-udp-size option sets the EDNS UDP size
that is advertised by named when querying the remote server.
Valid values are 512 to 4096 bytes (values outside this range will be
silently adjusted). This option is useful when you wish to
advertises a different value to this server than the value you
advertise globally, for example, when there is a firewall at the
remote site that is blocking large replies.

The max-udp-size option sets the
maximum EDNS UDP message size named will send. Valid
values are 512 to 4096 bytes (values outside this range will
be silently adjusted). This option is useful when you
know that there is a firewall that is blocking large
replies from named.

The server supports two zone transfer methods. The first, one-answer,
uses one DNS message per resource record transferred. many-answers packs
as many resource records as possible into a message. many-answers is
more efficient, but is only known to be understood by BIND 9, BIND
8.x, and patched versions of BIND
4.9.5. You can specify which method
to use for a server with the transfer-format option.
If transfer-format is not
specified, the transfer-format
specified
by the options statement will be
used.

transfers
is used to limit the number of concurrent inbound zone
transfers from the specified server. If no
transfers clause is specified, the
limit is set according to the
transfers-per-ns option.

The keys clause identifies a
key_id defined by the key statement,
to be used for transaction security (TSIG, the section called “TSIG”)
when talking to the remote server.
When a request is sent to the remote server, a request signature
will be generated using the key specified here and appended to the
message. A request originating from the remote server is not
required
to be signed by this key.

Although the grammar of the keys
clause
allows for multiple keys, only a single key per server is
currently
supported.

The transfer-source and
transfer-source-v6 clauses specify
the IPv4 and IPv6 source
address to be used for zone transfer with the remote server,
respectively.
For an IPv4 remote server, only transfer-source can
be specified.
Similarly, for an IPv6 remote server, only
transfer-source-v6 can be
specified.
For more details, see the description of
transfer-source and
transfer-source-v6 in
the section called “Zone Transfers”.

The notify-source and
notify-source-v6 clauses specify the
IPv4 and IPv6 source address to be used for notify
messages sent to remote servers, respectively. For an
IPv4 remote server, only notify-source
can be specified. Similarly, for an IPv6 remote server,
only notify-source-v6 can be specified.

The query-source and
query-source-v6 clauses specify the
IPv4 and IPv6 source address to be used for queries
sent to remote servers, respectively. For an IPv4
remote server, only query-source can
be specified. Similarly, for an IPv6 remote server,
only query-source-v6 can be specified.

The request-nsid clause determines
whether the local server will add a NSID EDNS option
to requests sent to the server. This overrides
request-nsid set at the view or
option level.

statistics-channels Statement Grammar

statistics-channels Statement Definition and
Usage

The statistics-channels statement
declares communication channels to be used by system
administrators to get access to statistics information of
the name server.

This statement intends to be flexible to support multiple
communication protocols in the future, but currently only
HTTP access is supported.
It requires that BIND 9 be compiled with libxml2;
the statistics-channels statement is
still accepted even if it is built without the library,
but any HTTP access will fail with an error.

An inet control channel is a TCP socket
listening at the specified ip_port on the
specified ip_addr, which can be an IPv4 or IPv6
address. An ip_addr of * (asterisk) is
interpreted as the IPv4 wildcard address; connections will be
accepted on any of the system's IPv4 addresses.
To listen on the IPv6 wildcard address,
use an ip_addr of ::.

If no port is specified, port 80 is used for HTTP channels.
The asterisk "*" cannot be used for
ip_port.

The attempt of opening a statistics channel is
restricted by the optional allow clause.
Connections to the statistics channel are permitted based on the
address_match_list.
If no allow clause is present,
named accepts connection
attempts from any address; since the statistics may
contain sensitive internal information, it is highly
recommended to restrict the source of connection requests
appropriately.

If no statistics-channels statement is present,
named will not open any communication channels.

trusted-keys Statement Grammar

trusted-keys Statement Definition
and Usage

The trusted-keys statement defines
DNSSEC security roots. DNSSEC is described in the section called “DNSSEC”. A security root is defined when the
public key for a non-authoritative zone is known, but
cannot be securely obtained through DNS, either because
it is the DNS root zone or because its parent zone is
unsigned. Once a key has been configured as a trusted
key, it is treated as if it had been validated and
proven secure. The resolver attempts DNSSEC validation
on all DNS data in subdomains of a security root.

All keys (and corresponding zones) listed in
trusted-keys are deemed to exist regardless
of what parent zones say. Similarly for all keys listed in
trusted-keys only those keys are
used to validate the DNSKEY RRset. The parent's DS RRset
will not be used.

The trusted-keys statement can contain
multiple key entries, each consisting of the key's
domain name, flags, protocol, algorithm, and the Base-64
representation of the key data.
Spaces, tabs, newlines and carriage returns are ignored
in the key data, so the configuration may be split up into
multiple lines.

trusted-keys may be set at the top level
of named.conf or within a view. If it is
set in both places, they are additive: keys defined at the top
level are inherited by all views, but keys defined in a view
are only used within that view.

managed-keys Statement Grammar

managed-keys Statement Definition
and Usage

The managed-keys statement, like
trusted-keys, defines DNSSEC
security roots. The difference is that
managed-keys can be kept up to date
automatically, without intervention from the resolver
operator.

Suppose, for example, that a zone's key-signing
key was compromised, and the zone owner had to revoke and
replace the key. A resolver which had the old key in a
trusted-keys statement would be
unable to validate this zone any longer; it would
reply with a SERVFAIL response code. This would
continue until the resolver operator had updated the
trusted-keys statement with the new key.

If, however, the zone were listed in a
managed-keys statement instead, then the
zone owner could add a "stand-by" key to the zone in advance.
named would store the stand-by key, and
when the original key was revoked, named
would be able to transition smoothly to the new key. It would
also recognize that the old key had been revoked, and cease
using that key to validate answers, minimizing the damage that
the compromised key could do.

A managed-keys statement contains a list of
the keys to be managed, along with information about how the
keys are to be initialized for the first time. The only
initialization method currently supported (as of
BIND 9.7.0) is initial-key.
This means the managed-keys statement must
contain a copy of the initializing key. (Future releases may
allow keys to be initialized by other methods, eliminating this
requirement.)

Consequently, a managed-keys statement
appears similar to a trusted-keys, differing
in the presence of the second field, containing the keyword
initial-key. The difference is, whereas the
keys listed in a trusted-keys continue to be
trusted until they are removed from
named.conf, an initializing key listed
in a managed-keys statement is only trusted
once: for as long as it takes to load the
managed key database and start the RFC 5011 key maintenance
process.

The first time named runs with a managed key
configured in named.conf, it fetches the
DNSKEY RRset directly from the zone apex, and validates it
using the key specified in the managed-keys
statement. If the DNSKEY RRset is validly signed, then it is
used as the basis for a new managed keys database.

From that point on, whenever named runs, it
sees the managed-keys statement, checks to
make sure RFC 5011 key maintenance has already been initialized
for the specified domain, and if so, it simply moves on. The
key specified in the managed-keys is not
used to validate answers; it has been superseded by the key or
keys stored in the managed keys database.

The next time named runs after a name
has been removed from the
managed-keys statement, the corresponding
zone will be removed from the managed keys database,
and RFC 5011 key maintenance will no longer be used for that
domain.

named only maintains a single managed keys
database; consequently, unlike trusted-keys,
managed-keys may only be set at the top
level of named.conf, not within a view.

In the current implementation, the managed keys database is
stored as a master-format zone file called
managed-keys.bind. When the key database
is changed, the zone is updated. As with any other dynamic
zone, changes will be written into a journal file,
managed-keys.bind.jnl. They are committed
to the master file as soon as possible afterward; in the case
of the managed key database, this will usually occur within 30
seconds. So, whenever named is using
automatic key maintenance, those two files can be expected to
exist in the working directory. (For this reason among others,
the working directory should be always be writable by
named.)

If the dnssec-validation option is
set to auto, named
will automatically initialize a managed key for the
root zone. Similarly, if the dnssec-lookaside
option is set to auto,
named will automatically initialize
a managed key for the zone dlv.isc.org.
In both cases, the key that is used to initialize the key
maintenance process is built into named,
and can be overridden from bindkeys-file.

view Statement Grammar

view Statement Definition and Usage

The view statement is a powerful
feature
of BIND 9 that lets a name server
answer a DNS query differently
depending on who is asking. It is particularly useful for
implementing
split DNS setups without having to run multiple servers.

Each view statement defines a view
of the
DNS namespace that will be seen by a subset of clients. A client
matches
a view if its source IP address matches the
address_match_list of the view's
match-clients clause and its
destination IP address matches
the address_match_list of the
view's
match-destinations clause. If not
specified, both
match-clients and match-destinations
default to matching all addresses. In addition to checking IP
addresses
match-clients and match-destinations
can also take keys which provide an
mechanism for the
client to select the view. A view can also be specified
as match-recursive-only, which
means that only recursive
requests from matching clients will match that view.
The order of the view statements is
significant —
a client request will be resolved in the context of the first
view that it matches.

Zones defined within a view
statement will
only be accessible to clients that match the view.
By defining a zone of the same name in multiple views, different
zone data can be given to different clients, for example,
"internal"
and "external" clients in a split DNS setup.

Many of the options given in the options statement
can also be used within a view
statement, and then
apply only when resolving queries with that view. When no
view-specific
value is given, the value in the options statement
is used as a default. Also, zone options can have default values
specified
in the view statement; these
view-specific defaults
take precedence over those in the options statement.

Views are class specific. If no class is given, class IN
is assumed. Note that all non-IN views must contain a hint zone,
since only the IN class has compiled-in default hints.

If there are no view statements in
the config
file, a default view that matches any client is automatically
created
in class IN. Any zone statements
specified on
the top level of the configuration file are considered to be part
of
this default view, and the options
statement will
apply to the default view. If any explicit view
statements are present, all zone
statements must
occur inside view statements.

Here is an example of a typical split DNS setup implemented
using view statements:

zone Statement Definition and Usage

Zone Types

master

The server has a master copy of the data
for the zone and will be able to provide authoritative
answers for
it.

slave

A slave zone is a replica of a master
zone. The masters list
specifies one or more IP addresses
of master servers that the slave contacts to update
its copy of the zone.
Masters list elements can also be names of other
masters lists.
By default, transfers are made from port 53 on the
servers; this can
be changed for all servers by specifying a port number
before the
list of IP addresses, or on a per-server basis after
the IP address.
Authentication to the master can also be done with
per-server TSIG keys.
If a file is specified, then the
replica will be written to this file whenever the zone
is changed,
and reloaded from this file on a server restart. Use
of a file is
recommended, since it often speeds server startup and
eliminates
a needless waste of bandwidth. Note that for large
numbers (in the
tens or hundreds of thousands) of zones per server, it
is best to
use a two-level naming scheme for zone filenames. For
example,
a slave server for the zone example.com might place
the zone contents into a file called
ex/example.com where ex/ is
just the first two letters of the zone name. (Most
operating systems
behave very slowly if you put 100000 files into
a single directory.)

stub

A stub zone is similar to a slave zone,
except that it replicates only the NS records of a
master zone instead
of the entire zone. Stub zones are not a standard part
of the DNS;
they are a feature specific to the BIND implementation.

Stub zones can be used to eliminate the need for glue
NS record
in a parent zone at the expense of maintaining a stub
zone entry and
a set of name server addresses in named.conf.
This usage is not recommended for new configurations,
and BIND 9
supports it only in a limited way.
In BIND 4/8, zone
transfers of a parent zone
included the NS records from stub children of that
zone. This meant
that, in some cases, users could get away with
configuring child stubs
only in the master server for the parent zone. BIND
9 never mixes together zone data from different zones
in this
way. Therefore, if a BIND 9 master serving a parent
zone has child stub zones configured, all the slave
servers for the
parent zone also need to have the same child stub
zones
configured.

Stub zones can also be used as a way of forcing the
resolution
of a given domain to use a particular set of
authoritative servers.
For example, the caching name servers on a private
network using
RFC1918 addressing may be configured with stub zones
for
10.in-addr.arpa
to use a set of internal name servers as the
authoritative
servers for that domain.

static-stub

A static-stub zone is similar to a stub zone
with the following exceptions:
the zone data is statically configured, rather
than transferred from a master server;
when recursion is necessary for a query that
matches a static-stub zone, the locally
configured data (nameserver names and glue addresses)
is always used even if different authoritative
information is cached.

The zone data is maintained in the form of NS
and (if necessary) glue A or AAAA RRs
internally, which can be seen by dumping zone
databases by rndc dumpdb -all.
The configured RRs are considered local configuration
parameters rather than public data.
Non recursive queries (i.e., those with the RD
bit off) to a static-stub zone are therefore
prohibited and will be responded with REFUSED.

Since the data is statically configured, no
zone maintenance action takes place for a static-stub
zone.
For example, there is no periodic refresh
attempt, and an incoming notify message
will be rejected with an rcode of NOTAUTH.

Each static-stub zone is configured with
internally generated NS and (if necessary)
glue A or AAAA RRs

forward

A "forward zone" is a way to configure
forwarding on a per-domain basis. A zone statement
of type forward can
contain a forward
and/or forwarders
statement,
which will apply to queries within the domain given by
the zone
name. If no forwarders
statement is present or
an empty list for forwarders is given, then no
forwarding will be done for the domain, canceling the
effects of
any forwarders in the options statement. Thus
if you want to use this type of zone to change the
behavior of the
global forward option
(that is, "forward first"
to, then "forward only", or vice versa, but want to
use the same
servers as set globally) you need to re-specify the
global forwarders.

hint

The initial set of root name servers is
specified using a "hint zone". When the server starts
up, it uses
the root hints to find a root name server and get the
most recent
list of root name servers. If no hint zone is
specified for class
IN, the server uses a compiled-in default set of root
servers hints.
Classes other than IN have no built-in defaults hints.

delegation-only

This is used to enforce the delegation-only
status of infrastructure zones (e.g. COM,
NET, ORG). Any answer that is received
without an explicit or implicit delegation
in the authority section will be treated
as NXDOMAIN. This does not apply to the
zone apex. This should not be applied to
leaf zones.

Class

The zone's name may optionally be followed by a class. If
a class is not specified, class IN (for Internet),
is assumed. This is correct for the vast majority of cases.

The hesiod class is
named for an information service from MIT's Project Athena. It
is
used to share information about various systems databases, such
as users, groups, printers and so on. The keyword
HS is
a synonym for hesiod.

Another MIT development is Chaosnet, a LAN protocol created
in the mid-1970s. Zone data for it can be specified with the CHAOS class.

Only meaningful if notify
is
active for this zone. The set of machines that will
receive a
DNS NOTIFY message
for this zone is made up of all the listed name servers
(other than
the primary master) for the zone plus any IP addresses
specified
with also-notify. A port
may be specified
with each also-notify
address to send the notify
messages to a port other than the default of 53.
also-notify is not
meaningful for stub zones.
The default is the empty list.

check-names

This option is used to restrict the character set and
syntax of
certain domain names in master files and/or DNS responses
received from the
network. The default varies according to zone type. For master zones the default is fail. For slave
zones the default is warn.
It is not implemented for hint zones.

Specify the type of database to be used for storing the
zone data. The string following the database keyword
is interpreted as a list of whitespace-delimited words.
The first word
identifies the database type, and any subsequent words are
passed
as arguments to the database to be interpreted in a way
specific
to the database type.

The default is "rbt", BIND 9's
native in-memory
red-black-tree database. This database does not take
arguments.

Other values are possible if additional database drivers
have been linked into the server. Some sample drivers are
included
with the distribution but none are linked in by default.

Only meaningful if the zone has a forwarders
list. The only value causes
the lookup to fail
after trying the forwarders and getting no answer, while first would
allow a normal lookup to be tried.

forwarders

Used to override the list of global forwarders.
If it is not specified in a zone of type forward,
no forwarding is done for the zone and the global options are
not used.

ixfr-base

Was used in BIND 8 to
specify the name
of the transaction log (journal) file for dynamic update
and IXFR.
BIND 9 ignores the option
and constructs the name of the journal
file by appending ".jnl"
to the name of the
zone file.

ixfr-tmp-file

Was an undocumented option in BIND 8.
Ignored in BIND 9.

journal

Allow the default journal's filename to be overridden.
The default is the zone's filename with ".jnl" appended.
This is applicable to master and slave zones.

In BIND 8, this option was
intended for specifying
a public zone key for verification of signatures in DNSSEC
signed
zones when they are loaded from disk. BIND 9 does not verify signatures
on load and ignores the option.

zone-statistics

If yes, the server will keep
statistical
information for this zone, which can be dumped to the
statistics-file defined in
the server options.

server-addresses

Only meaningful for static-stub zones.
This is a list of IP addresses to which queries
should be sent in recursive resolution for the
zone.
A non empty list for this option will internally
configure the apex NS RR with associated glue A or
AAAA RRs.

For example, if "example.com" is configured as a
static-stub zone with 192.0.2.1 and 2001:db8::1234
in a server-addresses option,
the following RRs will be internally configured.

These records are internally used to resolve
names under the static-stub zone.
For instance, if the server receives a query for
"www.example.com" with the RD bit on, the server
will initiate recursive resolution and send
queries to 192.0.2.1 and/or 2001:db8::1234.

server-names

Only meaningful for static-stub zones.
This is a list of domain names of nameservers that
act as authoritative servers of the static-stub
zone.
These names will be resolved to IP addresses when
named needs to send queries to
these servers.
To make this supplemental resolution successful,
these names must not be a subdomain of the origin
name of static-stub zone.
That is, when "example.net" is the origin of a
static-stub zone, "ns.example" and
"master.example.com" can be specified in the
server-names option, but
"ns.example.net" cannot, and will be rejected by
the configuration parser.

A non empty list for this option will internally
configure the apex NS RR with the specified names.
For example, if "example.com" is configured as a
static-stub zone with "ns1.example.net" and
"ns2.example.net"
in a server-names option,
the following RRs will be internally configured.

example.com. NS ns1.example.net.
example.com. NS ns2.example.net.

These records are internally used to resolve
names under the static-stub zone.
For instance, if the server receives a query for
"www.example.com" with the RD bit on, the server
initiate recursive resolution,
resolve "ns1.example.net" and/or
"ns2.example.net" to IP addresses, and then send
queries to (one or more of) these addresses.

auto-dnssec maintain; includes the
above, but also automatically adjusts the zone's DNSSEC
keys on schedule, according to the keys' timing metadata
(see dnssec-keygen(8) and
dnssec-settime(8)). The command
rndc sign
zonename causes
named to load keys from the key
repository and sign the zone with all keys that are
active.
rndc loadkeys
zonename causes
named to load keys from the key
repository and schedule key maintenance events to occur
in the future, but it does not sign the full zone
immediately. Note: once keys have been loaded for a
zone the first time, the repository will be searched
for changes periodically, regardless of whether
rndc loadkeys is used. The recheck
interval is hard-coded to
one hour.

auto-dnssec create; includes the
above, but also allows named
to create new keys in the key repository when needed.
(NOTE: This option is not yet implemented; the syntax is
being reserved for future use.)

Dynamic Update Policies

BIND 9 supports two alternative
methods of granting clients the right to perform
dynamic updates to a zone, configured by the
allow-update and
update-policy option, respectively.

The allow-update clause works the
same way as in previous versions of BIND.
It grants given clients the permission to update any
record of any name in the zone.

The update-policy clause
allows more fine-grained control over what updates are
allowed. A set of rules is specified, where each rule
either grants or denies permissions for one or more
names to be updated by one or more identities. If
the dynamic update request message is signed (that is,
it includes either a TSIG or SIG(0) record), the
identity of the signer can be determined.

Rules are specified in the update-policy
zone option, and are only meaningful for master zones.
When the update-policy statement
is present, it is a configuration error for the
allow-update statement to be
present. The update-policy statement
only examines the signer of a message; the source
address is not relevant.

There is a pre-defined update-policy
rule which can be switched on with the command
update-policy local;.
Switching on this rule in a zone causes
named to generate a TSIG session
key and place it in a file, and to allow that key
to update the zone. (By default, the file is
/var/run/named/session.key, the key
name is "local-ddns" and the key algorithm is HMAC-SHA256,
but these values are configurable with the
session-keyfile,
session-keyname and
session-keyalg options, respectively).

A client running on the local system, and with appropriate
permissions, may read that file and use the key to sign update
requests. The zone's update policy will be set to allow that
key to change any record within the zone. Assuming the
key name is "local-ddns", this policy is equivalent to:

update-policy { grant local-ddns zonesub any; };

The command nsupdate -l sends update
requests to localhost, and signs them using the session key.

Other rule definitions look like this:

( grant | deny ) identitynametype [name] [types]

Each rule grants or denies privileges. Once a message has
successfully matched a rule, the operation is immediately
granted or denied and no further rules are examined. A rule
is matched when the signer matches the identity field, the
name matches the name field in accordance with the nametype
field, and the type matches the types specified in the type
field.

No signer is required for tcp-self
or 6to4-self however the standard
reverse mapping / prefix conversion must match the identity
field.

The identity field specifies a name or a wildcard
name. Normally, this is the name of the TSIG or
SIG(0) key used to sign the update request. When a
TKEY exchange has been used to create a shared secret,
the identity of the shared secret is the same as the
identity of the key used to authenticate the TKEY
exchange. TKEY is also the negotiation method used
by GSS-TSIG, which establishes an identity that is
the Kerberos principal of the client, such as
"user@host.domain". When the
identity field specifies
a wildcard name, it is subject to DNS wildcard
expansion, so the rule will apply to multiple identities.
The identity field must
contain a fully-qualified domain name.

For nametypes krb5-self,
ms-self, krb5-subdomain,
and ms-subdomain the
identity field specifies
the Windows or Kerberos realm of the machine belongs to.

Exact-match semantics. This rule matches
when the name being updated is identical
to the contents of the
name field.

subdomain

This rule matches when the name being updated
is a subdomain of, or identical to, the
contents of the name
field.

zonesub

This rule is similar to subdomain, except that
it matches when the name being updated is a
subdomain of the zone in which the
update-policy statement
appears. This obviates the need to type the zone
name twice, and enables the use of a standard
update-policy statement in
multiple zones without modification.

When this rule is used, the
name field is omitted.

wildcard

The name field
is subject to DNS wildcard expansion, and
this rule matches when the name being updated
name is a valid expansion of the wildcard.

self

This rule matches when the name being updated
matches the contents of the
identity field.
The name field
is ignored, but should be the same as the
identity field.
The self nametype is
most useful when allowing using one key per
name to update, where the key has the same
name as the name to be updated. The
identity would
be specified as * (an asterisk) in
this case.

selfsub

This rule is similar to self
except that subdomains of self
can also be updated.

selfwild

This rule is similar to self
except that only subdomains of
self can be updated.

ms-self

This rule takes a Windows machine principal
(machine$@REALM) for machine in REALM and
and converts it machine.realm allowing the machine
to update machine.realm. The REALM to be matched
is specified in the identity
field.

ms-subdomain

This rule takes a Windows machine principal
(machine$@REALM) for machine in REALM and
converts it to machine.realm allowing the machine
to update subdomains of machine.realm. The REALM
to be matched is specified in the
identity field.

krb5-self

This rule takes a Kerberos machine principal
(host/machine@REALM) for machine in REALM and
and converts it machine.realm allowing the machine
to update machine.realm. The REALM to be matched
is specified in the identity
field.

krb5-subdomain

This rule takes a Kerberos machine principal
(host/machine@REALM) for machine in REALM and
converts it to machine.realm allowing the machine
to update subdomains of machine.realm. The REALM
to be matched is specified in the
identity field.

tcp-self

Allow updates that have been sent via TCP and
for which the standard mapping from the initiating
IP address into the IN-ADDR.ARPA and IP6.ARPA
namespaces match the name to be updated.

Note

It is theoretically possible to spoof these TCP
sessions.

6to4-self

Allow the 6to4 prefix to be update by any TCP
connection from the 6to4 network or from the
corresponding IPv4 address. This is intended
to allow NS or DNAME RRsets to be added to the
reverse tree.

Note

It is theoretically possible to spoof these TCP
sessions.

external

This rule allows named
to defer the decision of whether to allow a
given update to an external daemon.

The method of communicating with the daemon is
specified in the identity
field, the format of which is
"local:path",
where path is the location
of a UNIX-domain socket. (Currently, "local" is the
only supported mechanism.)

Requests to the external daemon are sent over the
UNIX-domain socket as datagrams with the following
format:

The daemon replies with a four-byte value in
network byte order, containing either 0 or 1; 0
indicates that the specified update is not
permitted, and 1 indicates that it is.

In all cases, the name
field must specify a fully-qualified domain name.

If no types are explicitly specified, this rule matches
all types except RRSIG, NS, SOA, NSEC and NSEC3. Types
may be specified by name, including "ANY" (ANY matches
all types except NSEC and NSEC3, which can never be
updated). Note that when an attempt is made to delete
all records associated with a name, the rules are
checked for each existing record type.

Zone File

Types of Resource Records and When to Use Them

This section, largely borrowed from RFC 1034, describes the
concept of a Resource Record (RR) and explains when each is used.
Since the publication of RFC 1034, several new RRs have been
identified
and implemented in the DNS. These are also included.

Resource Records

A domain name identifies a node. Each node has a set of
resource information, which may be empty. The set of resource
information associated with a particular name is composed of
separate RRs. The order of RRs in a set is not significant and
need not be preserved by name servers, resolvers, or other
parts of the DNS. However, sorting of multiple RRs is
permitted for optimization purposes, for example, to specify
that a particular nearby server be tried first. See the section called “The sortlist Statement” and the section called “RRset Ordering”.

The components of a Resource Record are:

owner name

The domain name where the RR is found.

type

An encoded 16-bit value that specifies
the type of the resource record.

TTL

The time-to-live of the RR. This field
is a 32-bit integer in units of seconds, and is
primarily used by
resolvers when they cache RRs. The TTL describes how
long a RR can
be cached before it should be discarded.

class

An encoded 16-bit value that identifies
a protocol family or instance of a protocol.

RDATA

The resource data. The format of the
data is type (and sometimes class) specific.

The following are types of valid RRs:

A

A host address. In the IN class, this is a
32-bit IP address. Described in RFC 1035.

AAAA

IPv6 address. Described in RFC 1886.

A6

IPv6 address. This can be a partial
address (a suffix) and an indirection to the name
where the rest of the
address (the prefix) can be found. Experimental.
Described in RFC 2874.

AFSDB

Location of AFS database servers.
Experimental. Described in RFC 1183.

APL

Address prefix list. Experimental.
Described in RFC 3123.

CERT

Holds a digital certificate.
Described in RFC 2538.

CNAME

Identifies the canonical name of an alias.
Described in RFC 1035.

DHCID

Is used for identifying which DHCP client is
associated with this name. Described in RFC 4701.

DNAME

Replaces the domain name specified with
another name to be looked up, effectively aliasing an
entire
subtree of the domain name space rather than a single
record
as in the case of the CNAME RR.
Described in RFC 2672.

DNSKEY

Stores a public key associated with a signed
DNS zone. Described in RFC 4034.

DS

Stores the hash of a public key associated with a
signed DNS zone. Described in RFC 4034.

GPOS

Specifies the global position. Superseded by LOC.

HINFO

Identifies the CPU and OS used by a host.
Described in RFC 1035.

IPSECKEY

Provides a method for storing IPsec keying material in
DNS. Described in RFC 4025.

ISDN

Representation of ISDN addresses.
Experimental. Described in RFC 1183.

KEY

Stores a public key associated with a
DNS name. Used in original DNSSEC; replaced
by DNSKEY in DNSSECbis, but still used with
SIG(0). Described in RFCs 2535 and 2931.

KX

Identifies a key exchanger for this
DNS name. Described in RFC 2230.

LOC

For storing GPS info. Described in RFC 1876.
Experimental.

MX

Identifies a mail exchange for the domain with
a 16-bit preference value (lower is better)
followed by the host name of the mail exchange.
Described in RFC 974, RFC 1035.

NAPTR

Name authority pointer. Described in RFC 2915.

NSAP

A network service access point.
Described in RFC 1706.

NS

The authoritative name server for the
domain. Described in RFC 1035.

NSEC

Used in DNSSECbis to securely indicate that
RRs with an owner name in a certain name interval do
not exist in
a zone and indicate what RR types are present for an
existing name.
Described in RFC 4034.

NSEC3

Used in DNSSECbis to securely indicate that
RRs with an owner name in a certain name
interval do not exist in a zone and indicate
what RR types are present for an existing
name. NSEC3 differs from NSEC in that it
prevents zone enumeration but is more
computationally expensive on both the server
and the client than NSEC. Described in RFC
5155.

NSEC3PARAM

Used in DNSSECbis to tell the authoritative
server which NSEC3 chains are available to use.
Described in RFC 5155.

NXT

Used in DNSSEC to securely indicate that
RRs with an owner name in a certain name interval do
not exist in
a zone and indicate what RR types are present for an
existing name.
Used in original DNSSEC; replaced by NSEC in
DNSSECbis.
Described in RFC 2535.

PTR

A pointer to another part of the domain
name space. Described in RFC 1035.

PX

Provides mappings between RFC 822 and X.400
addresses. Described in RFC 2163.

RP

Information on persons responsible
for the domain. Experimental. Described in RFC 1183.

RRSIG

Contains DNSSECbis signature data. Described
in RFC 4034.

RT

Route-through binding for hosts that
do not have their own direct wide area network
addresses.
Experimental. Described in RFC 1183.

SIG

Contains DNSSEC signature data. Used in
original DNSSEC; replaced by RRSIG in
DNSSECbis, but still used for SIG(0).
Described in RFCs 2535 and 2931.

SOA

Identifies the start of a zone of authority.
Described in RFC 1035.

SPF

Contains the Sender Policy Framework information
for a given email domain. Described in RFC 4408.

SRV

Information about well known network
services (replaces WKS). Described in RFC 2782.

SSHFP

Provides a way to securely publish a secure shell key's
fingerprint. Described in RFC 4255.

TXT

Text records. Described in RFC 1035.

WKS

Information about which well known
network services, such as SMTP, that a domain
supports. Historical.

X25

Representation of X.25 network addresses.
Experimental. Described in RFC 1183.

The following classes of resource records
are currently valid in the DNS:

IN

The Internet.

CH

Chaosnet, a LAN protocol created at MIT in the
mid-1970s.
Rarely used for its historical purpose, but reused for
BIND's
built-in server information zones, e.g.,
version.bind.

HS

Hesiod, an information service
developed by MIT's Project Athena. It is used to share
information
about various systems databases, such as users,
groups, printers
and so on.

The owner name is often implicit, rather than forming an
integral
part of the RR. For example, many name servers internally form
tree
or hash structures for the name space, and chain RRs off nodes.
The remaining RR parts are the fixed header (type, class, TTL)
which is consistent for all RRs, and a variable part (RDATA)
that
fits the needs of the resource being described.

The meaning of the TTL field is a time limit on how long an
RR can be kept in a cache. This limit does not apply to
authoritative
data in zones; it is also timed out, but by the refreshing
policies
for the zone. The TTL is assigned by the administrator for the
zone where the data originates. While short TTLs can be used to
minimize caching, and a zero TTL prohibits caching, the
realities
of Internet performance suggest that these times should be on
the
order of days for the typical host. If a change can be
anticipated,
the TTL can be reduced prior to the change to minimize
inconsistency
during the change, and then increased back to its former value
following
the change.

The data in the RDATA section of RRs is carried as a combination
of binary strings and domain names. The domain names are
frequently
used as "pointers" to other data in the DNS.

Textual expression of RRs

RRs are represented in binary form in the packets of the DNS
protocol, and are usually represented in highly encoded form
when
stored in a name server or resolver. In the examples provided
in
RFC 1034, a style similar to that used in master files was
employed
in order to show the contents of RRs. In this format, most RRs
are shown on a single line, although continuation lines are
possible
using parentheses.

The start of the line gives the owner of the RR. If a line
begins with a blank, then the owner is assumed to be the same as
that of the previous RR. Blank lines are often included for
readability.

Following the owner, we list the TTL, type, and class of the
RR. Class and type use the mnemonics defined above, and TTL is
an integer before the type field. In order to avoid ambiguity
in
parsing, type and class mnemonics are disjoint, TTLs are
integers,
and the type mnemonic is always last. The IN class and TTL
values
are often omitted from examples in the interests of clarity.

The resource data or RDATA section of the RR are given using
knowledge of the typical representation for the data.

For example, we might show the RRs carried in a message as:

ISI.EDU.

MX

10 VENERA.ISI.EDU.

MX

10 VAXA.ISI.EDU

VENERA.ISI.EDU

A

128.9.0.32

A

10.1.0.52

VAXA.ISI.EDU

A

10.2.0.27

A

128.9.0.33

The MX RRs have an RDATA section which consists of a 16-bit
number followed by a domain name. The address RRs use a
standard
IP address format to contain a 32-bit internet address.

The above example shows six RRs, with two RRs at each of three
domain names.

Similarly we might see:

XX.LCS.MIT.EDU.

IN A

10.0.0.44

CH A

MIT.EDU. 2420

This example shows two addresses for
XX.LCS.MIT.EDU, each of a different class.

Discussion of MX Records

As described above, domain servers store information as a
series of resource records, each of which contains a particular
piece of information about a given domain name (which is usually,
but not always, a host). The simplest way to think of a RR is as
a typed pair of data, a domain name matched with a relevant datum,
and stored with some additional type information to help systems
determine when the RR is relevant.

MX records are used to control delivery of email. The data
specified in the record is a priority and a domain name. The
priority
controls the order in which email delivery is attempted, with the
lowest number first. If two priorities are the same, a server is
chosen randomly. If no servers at a given priority are responding,
the mail transport agent will fall back to the next largest
priority.
Priority numbers do not have any absolute meaning — they are
relevant
only respective to other MX records for that domain name. The
domain
name given is the machine to which the mail will be delivered.
It must have an associated address record
(A or AAAA) — CNAME is not sufficient.

For a given domain, if there is both a CNAME record and an
MX record, the MX record is in error, and will be ignored.
Instead,
the mail will be delivered to the server specified in the MX
record
pointed to by the CNAME.
For example:

example.com.

IN

MX

10

mail.example.com.

IN

MX

10

mail2.example.com.

IN

MX

20

mail.backup.org.

mail.example.com.

IN

A

10.0.0.1

mail2.example.com.

IN

A

10.0.0.2

Mail delivery will be attempted to mail.example.com and
mail2.example.com (in
any order), and if neither of those succeed, delivery to mail.backup.org will
be attempted.

Setting TTLs

The time-to-live of the RR field is a 32-bit integer represented
in units of seconds, and is primarily used by resolvers when they
cache RRs. The TTL describes how long a RR can be cached before it
should be discarded. The following three types of TTL are
currently
used in a zone file.

SOA

The last field in the SOA is the negative
caching TTL. This controls how long other servers will
cache no-such-domain
(NXDOMAIN) responses from you.

The maximum time for
negative caching is 3 hours (3h).

$TTL

The $TTL directive at the top of the
zone file (before the SOA) gives a default TTL for every
RR without
a specific TTL set.

RR TTLs

Each RR can have a TTL as the second
field in the RR, which will control how long other
servers can cache it.

All of these TTLs default to units of seconds, though units
can be explicitly specified, for example, 1h30m.

Inverse Mapping in IPv4

Reverse name resolution (that is, translation from IP address
to name) is achieved by means of the in-addr.arpa domain
and PTR records. Entries in the in-addr.arpa domain are made in
least-to-most significant order, read left to right. This is the
opposite order to the way IP addresses are usually written. Thus,
a machine with an IP address of 10.1.2.3 would have a
corresponding
in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record
whose data field is the name of the machine or, optionally,
multiple
PTR records if the machine has more than one name. For example,
in the [example.com] domain:

$ORIGIN

2.1.10.in-addr.arpa

3

IN PTR foo.example.com.

Note

The $ORIGIN lines in the examples
are for providing context to the examples only — they do not
necessarily
appear in the actual usage. They are only used here to indicate
that the example is relative to the listed origin.

Other Zone File Directives

The Master File Format was initially defined in RFC 1035 and
has subsequently been extended. While the Master File Format
itself
is class independent all records in a Master File must be of the
same
class.

Master File Directives include $ORIGIN, $INCLUDE,
and $TTL.

The @ (at-sign)

When used in the label (or name) field, the asperand or
at-sign (@) symbol represents the current origin.
At the start of the zone file, it is the
<zone_name> (followed by
trailing dot).

The $ORIGIN Directive

Syntax: $ORIGINdomain-name
[comment]

$ORIGIN
sets the domain name that will be appended to any
unqualified records. When a zone is first read in there
is an implicit $ORIGIN
<zone_name>.
(followed by trailing dot).
The current $ORIGIN is appended to
the domain specified in the $ORIGIN
argument if it is not absolute.

$ORIGIN example.com.
WWW CNAME MAIN-SERVER

is equivalent to

WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.

The $INCLUDE Directive

Syntax: $INCLUDEfilename
[origin]
[comment]

Read and process the file filename as
if it were included into the file at this point. If origin is
specified the file is processed with $ORIGIN set
to that value, otherwise the current $ORIGIN is
used.

The origin and the current domain name
revert to the values they had prior to the $INCLUDE once
the file has been read.

Note

RFC 1035 specifies that the current origin should be restored
after
an $INCLUDE, but it is silent
on whether the current
domain name should also be restored. BIND 9 restores both of
them.
This could be construed as a deviation from RFC 1035, a
feature, or both.

The $TTL Directive

Syntax: $TTLdefault-ttl
[comment]

Set the default Time To Live (TTL) for subsequent records
with undefined TTLs. Valid TTLs are of the range 0-2147483647
seconds.

$TTL
is defined in RFC 2308.

BIND Master File Extension: the $GENERATE Directive

Syntax: $GENERATErangelhs
[ttl]
[class]
typerhs
[comment]

$GENERATE
is used to create a series of resource records that only
differ from each other by an
iterator. $GENERATE can be used to
easily generate the sets of records required to support
sub /24 reverse delegations described in RFC 2317:
Classless IN-ADDR.ARPA delegation.

This can be one of two forms: start-stop
or start-stop/step. If the first form is used, then step
is set to 1. start, stop and step must be positive
integers between 0 and (2^31)-1. start must not be
larger than stop.

lhs

This
describes the owner name of the resource records
to be created. Any single $
(dollar sign)
symbols within the lhs string
are replaced by the iterator value.
To get a $ in the output, you need to escape the
$ using a backslash
\,
e.g. \$. The
$ may optionally be followed
by modifiers which change the offset from the
iterator, field width and base.
Modifiers are introduced by a
{ (left brace) immediately following the
$ as
${offset[,width[,base]]}.
For example, ${-20,3,d}
subtracts 20 from the current value, prints the
result as a decimal in a zero-padded field of
width 3.
Available output forms are decimal
(d), octal
(o), hexadecimal
(x or X
for uppercase) and nibble
(n or N\
for uppercase). The default modifier is
${0,0,d}. If the
lhs is not absolute, the
current $ORIGIN is appended
to the name.

In nibble mode the value will be treated as
if it was a reversed hexadecimal string
with each hexadecimal digit as a separate
label. The width field includes the label
separator.

For compatibility with earlier versions,
$$ is still recognized as
indicating a literal $ in the output.

ttl

Specifies the time-to-live of the generated records. If
not specified this will be inherited using the
normal TTL inheritance rules.

class
and ttl can be
entered in either order.

class

Specifies the class of the generated records.
This must match the zone class if it is
specified.

class
and ttl can be
entered in either order.

type

Any valid type.

rhs

rhs, optionally, quoted string.

The $GENERATE directive is a BIND extension
and not part of the standard zone file format.

BIND 8 does not support the optional TTL and CLASS fields.

Additional File Formats

In addition to the standard textual format, BIND 9
supports the ability to read or dump to zone files in
other formats. The raw format is
currently available as an additional format. It is a
binary format representing BIND 9's internal data
structure directly, thereby remarkably improving the
loading time.

For a primary server, a zone file in the
raw format is expected to be
generated from a textual zone file by the
named-compilezone command. For a
secondary server or for a dynamic zone, it is automatically
generated (if this format is specified by the
masterfile-format option) when
named dumps the zone contents after
zone transfer or when applying prior updates.

If a zone file in a binary format needs manual modification,
it first must be converted to a textual form by the
named-compilezone command. All
necessary modification should go to the text file, which
should then be converted to the binary form by the
named-compilezone command again.

Although the raw format uses the
network byte order and avoids architecture-dependent
data alignment so that it is as much portable as
possible, it is primarily expected to be used inside
the same single system. In order to export a zone
file in the raw format or make a
portable backup of the file, it is recommended to
convert the file to the standard textual representation.

BIND9 Statistics

BIND 9 maintains lots of statistics
information and provides several interfaces for users to
get access to the statistics.
The available statistics include all statistics counters
that were available in BIND 8 and
are meaningful in BIND 9,
and other information that is considered useful.

The statistics information is categorized into the following
sections.

Incoming Requests

The number of incoming DNS requests for each OPCODE.

Incoming Queries

The number of incoming queries for each RR type.

Outgoing Queries

The number of outgoing queries for each RR
type sent from the internal resolver.
Maintained per view.

Statistics counters about name resolution
performed in the internal resolver.
Maintained per view.

Cache DB RRsets

The number of RRsets per RR type and nonexistent
names stored in the cache database.
If the exclamation mark (!) is printed for a RR
type, it means that particular type of RRset is
known to be nonexistent (this is also known as
"NXRRSET").
Maintained per view.

Socket I/O Statistics

Statistics counters about network related events.

A subset of Name Server Statistics is collected and shown
per zone for which the server has the authority when
zone-statistics is set to
yes.
These statistics counters are shown with their zone and view
names.
In some cases the view names are omitted for the default view.

There are currently two user interfaces to get access to the
statistics.
One is in the plain text format dumped to the file specified
by the statistics-file configuration option.
The other is remotely accessible via a statistics channel
when the statistics-channels statement
is specified in the configuration file
(see the section called “statistics-channels Statement Grammar”.)

The Statistics File

The text format statistics dump begins with a line, like:

+++ Statistics Dump +++ (973798949)

The number in parentheses is a standard
Unix-style timestamp, measured as seconds since January 1, 1970.
Following
that line is a set of statistics information, which is categorized
as described above.
Each section begins with a line, like:

++ Name Server Statistics ++

Each section consists of lines, each containing the statistics
counter value followed by its textual description.
See below for available counters.
For brevity, counters that have a value of 0 are not shown
in the statistics file.

The statistics dump ends with the line where the
number is identical to the number in the beginning line; for example:

--- Statistics Dump --- (973798949)

Statistics Counters

The following tables summarize statistics counters that
BIND 9 provides.
For each row of the tables, the leftmost column is the
abbreviated symbol name of that counter.
These symbols are shown in the statistics information
accessed via an HTTP statistics channel.
The rightmost column gives the description of the counter,
which is also shown in the statistics file
(but, in this document, possibly with slight modification
for better readability).
Additional notes may also be provided in this column.
When a middle column exists between these two columns,
it gives the corresponding counter name of the
BIND 8 statistics, if applicable.

Name Server Statistics Counters

Symbol

BIND8 Symbol

Description

Requestv4

RQ

IPv4 requests received.
Note: this also counts non query requests.

Requestv6

RQ

IPv6 requests received.
Note: this also counts non query requests.

ReqEdns0

Requests with EDNS(0) received.

ReqBadEDNSVer

Requests with unsupported EDNS version received.

ReqTSIG

Requests with TSIG received.

ReqSIG0

Requests with SIG(0) received.

ReqBadSIG

Requests with invalid (TSIG or SIG(0)) signature.

ReqTCP

RTCP

TCP requests received.

AuthQryRej

RUQ

Authoritative (non recursive) queries rejected.

RecQryRej

RURQ

Recursive queries rejected.

XfrRej

RUXFR

Zone transfer requests rejected.

UpdateRej

RUUpd

Dynamic update requests rejected.

Response

SAns

Responses sent.

RespTruncated

Truncated responses sent.

RespEDNS0

Responses with EDNS(0) sent.

RespTSIG

Responses with TSIG sent.

RespSIG0

Responses with SIG(0) sent.

QrySuccess

Queries resulted in a successful answer.
This means the query which returns a NOERROR response
with at least one answer RR.
This corresponds to the
success counter
of previous versions of
BIND 9.

QryAuthAns

Queries resulted in authoritative answer.

QryNoauthAns

SNaAns

Queries resulted in non authoritative answer.

QryReferral

Queries resulted in referral answer.
This corresponds to the
referral counter
of previous versions of
BIND 9.

QryNxrrset

Queries resulted in NOERROR responses with no data.
This corresponds to the
nxrrset counter
of previous versions of
BIND 9.

QrySERVFAIL

SFail

Queries resulted in SERVFAIL.

QryFORMERR

SFErr

Queries resulted in FORMERR.

QryNXDOMAIN

SNXD

Queries resulted in NXDOMAIN.
This corresponds to the
nxdomain counter
of previous versions of
BIND 9.

QryRecursion

RFwdQ

Queries which caused the server
to perform recursion in order to find the final answer.
This corresponds to the
recursion counter
of previous versions of
BIND 9.

QryDuplicate

RDupQ

Queries which the server attempted to
recurse but discovered an existing query with the same
IP address, port, query ID, name, type and class
already being processed.
This corresponds to the
duplicate counter
of previous versions of
BIND 9.

QryDropped

Recursive queries for which the server
discovered an excessive number of existing
recursive queries for the same name, type and
class and were subsequently dropped.
This is the number of dropped queries due to
the reason explained with the
clients-per-query
and
max-clients-per-query
options
(see the description about
clients-per-query.)
This corresponds to the
dropped counter
of previous versions of
BIND 9.

QryFailure

Other query failures.
This corresponds to the
failure counter
of previous versions of
BIND 9.
Note: this counter is provided mainly for
backward compatibility with the previous versions.
Normally a more fine-grained counters such as
AuthQryRej and
RecQryRej
that would also fall into this counter are provided,
and so this counter would not be of much
interest in practice.

XfrReqDone

Requested zone transfers completed.

UpdateReqFwd

Update requests forwarded.

UpdateRespFwd

Update responses forwarded.

UpdateFwdFail

Dynamic update forward failed.

UpdateDone

Dynamic updates completed.

UpdateFail

Dynamic updates failed.

UpdateBadPrereq

Dynamic updates rejected due to prerequisite failure.

RPZRewrites

Response policy zone rewrites.

Zone Maintenance Statistics Counters

Symbol

Description

NotifyOutv4

IPv4 notifies sent.

NotifyOutv6

IPv6 notifies sent.

NotifyInv4

IPv4 notifies received.

NotifyInv6

IPv6 notifies received.

NotifyRej

Incoming notifies rejected.

SOAOutv4

IPv4 SOA queries sent.

SOAOutv6

IPv6 SOA queries sent.

AXFRReqv4

IPv4 AXFR requested.

AXFRReqv6

IPv6 AXFR requested.

IXFRReqv4

IPv4 IXFR requested.

IXFRReqv6

IPv6 IXFR requested.

XfrSuccess

Zone transfer requests succeeded.

XfrFail

Zone transfer requests failed.

Resolver Statistics Counters

Symbol

BIND8 Symbol

Description

Queryv4

SFwdQ

IPv4 queries sent.

Queryv6

SFwdQ

IPv6 queries sent.

Responsev4

RR

IPv4 responses received.

Responsev6

RR

IPv6 responses received.

NXDOMAIN

RNXD

NXDOMAIN received.

SERVFAIL

RFail

SERVFAIL received.

FORMERR

RFErr

FORMERR received.

OtherError

RErr

Other errors received.

EDNS0Fail

EDNS(0) query failures.

Mismatch

RDupR

Mismatch responses received.
The DNS ID, response's source address,
and/or the response's source port does not
match what was expected.
(The port must be 53 or as defined by
the port option.)
This may be an indication of a cache
poisoning attempt.

Truncated

Truncated responses received.

Lame

RLame

Lame delegations received.

Retry

SDupQ

Query retries performed.

QueryAbort

Queries aborted due to quota control.

QuerySockFail

Failures in opening query sockets.
One common reason for such failures is a
failure of opening a new socket due to a
limitation on file descriptors.

QueryTimeout

Query timeouts.

GlueFetchv4

SSysQ

IPv4 NS address fetches invoked.

GlueFetchv6

SSysQ

IPv6 NS address fetches invoked.

GlueFetchv4Fail

IPv4 NS address fetch failed.

GlueFetchv6Fail

IPv6 NS address fetch failed.

ValAttempt

DNSSEC validation attempted.

ValOk

DNSSEC validation succeeded.

ValNegOk

DNSSEC validation on negative information succeeded.

ValFail

DNSSEC validation failed.

QryRTTnn

Frequency table on round trip times (RTTs) of
queries.
Each nn specifies the corresponding
frequency.
In the sequence of
nn_1,
nn_2,
...,
nn_m,
the value of nn_i is the
number of queries whose RTTs are between
nn_(i-1) (inclusive) and
nn_i (exclusive) milliseconds.
For the sake of convenience we define
nn_0 to be 0.
The last entry should be represented as
nn_m+, which means the
number of queries whose RTTs are equal to or over
nn_m milliseconds.

Socket I/O Statistics Counters

Socket I/O statistics counters are defined per socket
types, which are
UDP4 (UDP/IPv4),
UDP6 (UDP/IPv6),
TCP4 (TCP/IPv4),
TCP6 (TCP/IPv6),
Unix (Unix Domain), and
FDwatch (sockets opened outside the
socket module).
In the following table <TYPE>
represents a socket type.
Not all counters are available for all socket types;
exceptions are noted in the description field.

Symbol

Description

<TYPE>Open

Sockets opened successfully.
This counter is not applicable to the
FDwatch type.

<TYPE>OpenFail

Failures of opening sockets.
This counter is not applicable to the
FDwatch type.

<TYPE>Close

Sockets closed.

<TYPE>BindFail

Failures of binding sockets.

<TYPE>ConnFail

Failures of connecting sockets.

<TYPE>Conn

Connections established successfully.

<TYPE>AcceptFail

Failures of accepting incoming connection requests.
This counter is not applicable to the
UDP and
FDwatch types.

<TYPE>Accept

Incoming connections successfully accepted.
This counter is not applicable to the
UDP and
FDwatch types.